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Home Made Keel Design Questions

4K views 25 replies 9 participants last post by  CaptainFaris 
#1 ·
I've read many "keel" design related threads in various forums. Yet I persist in dreaming up a revolutionary new hull design for a homemade plywood sailboat. I can't find anyone with experience in testing my "keel-less" hull concept; so I thought I'd ask specific questions:

1. The flat sides of a plywood scow or barge sailboat could simply extend straight down a foot or three and function as fixed or permanent "leeboards". Sure there's the debate about wetted surface and length and depth and effectiveness and drag... But has anyone done this?

2. "Fins" or horizontal skegs could be mounted on the above mentioned side/keels in such a way as to "lift" the lee/heeled down side of the boat. That is, a fixed horizontal "trim plane" could project along the side of the flat sided boat with little or now portion under water when "level" but all of it under water when heeled over, creating a downward deadrise (? term) on the lee side when heeled over and thus lifting the boat--instead of using ballast on the windward side to press down and creating a righting moment.

I thought of these items by comparing outriggers and "M" shaped hulls and speculating about using hydrodynamics to lift or push up on the lee side. Size and shape and angle of these horizontal stabilizers would need to be determined by trial and error, I believe.

I'm trying to create the least displacement 14 ft sailing dinghy or scow or skiff possible that will still support a maximum amount of sail area without capsizing. I figure I could trade the drag from extra displacement for the drag of this crazy hull.

Note: My "actual" hull shape encapsulates these two elements (twin keel-like vertical sides plus fixed trim plane/fins) into a space-age "body" by enclosed some "space" above the fins with flotation voids and other skins just like Star Wars spaceships all have aerodynamic shells even though they are useless in space.

But if the whole thing just flips upside down and embarrasses me, I might continue to cut out paper models of alternatives until everyone stops mocking me here...

Thanks,
Phil
 
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#2 · (Edited)
The simple formulation is what's called a bilge keel, basically where the chine I sail there is a runner that stretches for and aft to prevent slippage. They have lots of wetted surface, add lots of drag, but allow for very shallow water operation. They are fine for slow boats that don the mind pointing low.

The more complicated option where you suggest using lifting foils is pretty much what the Quant 23 has done. But the foils are short (bow to stern), deep, and very high aspect to maximize lift and minimize drag.
 
#3 ·
Many multihulls use the ideas you've presented here. The flat straight outer sides of the sponsons of some trimarans allow them to go better to windward than the more rounded ones.
Piver used fins on the sponsons of his first generation tris, but added multiple hard chines on his later AA series.
But what works on a multihull probably won't on the heavier monohull. A well designed multihull rides primarily on the surface of the water, unlike a mono which must move through it. This allows for more radical designs as there is so much less strength required to skim on the surface.
There are a lot of hard chine monos out there which do use the chines to help prevent leeway. However, adding a fin to a chine would probably act more as a stabilizer than against leeway. Certainly, the more the boat heels, the less efficient those fins will be.
I think you are searching for something similar to foils, which are in their infancy at this point. I would love to see the advancements in that tech in 20 or 30 years, but alas that will never happen.
 
#4 ·
It is hard to "see" what I am really talking about, I'm sure. But bilge keels are totally different in that they are ballasted and fairly short and aren't attached at the chine. And the hydrofoil Quant boats aren't displacement boats at all.

I'm just thinking of vertical sides that extend deep below the water while the flat bottom floats only inches deep. And the lift fins aren't foils, just a fixed "trim tab" that runs down the length of the boat's side, only touching water when heeled over.

I'll finish building my tiny test vessel, run some tests, and report as to whether or not this method works for dinghy construction out of plywood.

As I said, this scheme is just to allow lightweight dinghies or scows to carry much more sail area (and rigging).

A few hundred dollars on a prototype can only be a "learning experience". I can always throw a bunch of sand bags into the boat to hold it down in a gale...
 
#5 · (Edited)
It is hard to "see" what I am really talking about, I'm sure. But bilge keels are totally different in that they are ballasted and fairly short and aren't attached at the chine. And the hydrofoil Quant boats aren't displacement boats at all.

I'm just thinking of vertical sides that extend deep below the water while the flat bottom floats only inches deep. And the lift fins aren't foils, just a fixed "trim tab" that runs down the length of the boat's side, only touching water when heeled over.

I'll finish building my tiny test vessel, run some tests, and report as to whether or not this method works for dinghy construction out of plywood.

As I said, this scheme is just to allow lightweight dinghies or scows to carry much more sail area (and rigging).

A few hundred dollars on a prototype can only be a "learning experience". I can always throw a bunch of sand bags into the boat to hold it down in a gale...
For some weird reason it's still called a bilge keel even if it is unballasted. Also google chine-runner.
 

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#9 · (Edited)
As soon as you heel, these Sides" as you refer to them will drastically lose their efficiency, if I understand you correctly. They will also seriously hamper the boat's turning ability, I believe. A centerboard or keel is a point around which a boat can turn, but I don't see that in your design.
 
#8 ·
What direction am I supposed to look at that from? Is that a side view, bottom veiw?
Not trying to be negative but I can't figure out what I'm looking at.
Maybe you should try some of your ideas out as an RC sailboat. Seen some pretty wild sailboats in the "open" classes where length and sail area are the only constraints. Since you wouldn't be racing it you could do anything you want.
 
#10 ·
Regarding heeling and the sides/chines/skegs/twin-keels "losing efficiency": That's a good consideration, and one that I have fully considered. First, all keels lose efficiency by tilting away from vertical when heeled (except twin or bilge keels). In my model these show up as vertical and they would slightly shorten in lateral resistance. The windward side/chine would come out of the water but the leeward would go deeper. Also, the "real" version will have 20 degree outward tilt and therefore they'd be getting both deeper and more vertical when heeled. Second, while they are "short" and "shoal draft" style keels or twin keels, they have extra lateral resistance due to "area". Interestingly, calculations of keel efficiency show that the leading edges are more effective than trailing, so a long keel would be inefficient by some unknown (unless you're a hydrodynamics engineer) percent. Yet sheer quantity can compensate. Third, that "quantity" compensation actually adds to wetted surface, true, yet calculations of drag from wetted surface are "inconsistent" between engineers. So I opt to just try it out in the real world. Fourth, "fast tacking" is impinged upon by all long keels and these are probably extra "good" for tracking (and therefore bad for tacking). But enlarged rudders have been documented as ways to force tacking in such "good tracking" hulls configurations. Again, trials in the real world will provide answers. I actually expect to trim and shape the length and depth of these "sides" until they permit fast tacking.

My goal for this small boat, besides being an experiment in hull design, is to "support" large sails that need plenty of "work" to handle, thus creating a "training vessel" to teach crews how to coordinate their trimming tasks with a skipper who is calculating course and wind direction. I have a narrow stretch of river behind a dam near my house and only a very small boat can be used--so I'm packing as much training into a single dinghy/skiff sized shoal-draft, non-ballasted sailboat as possible. Uh, I'm afraid to admit that this will also be tested in a schooner variant, with two masts and both jib and staysail up front on a bowsprit. Yeah, it's a crazy experiment--but it might actually work. At least it will be educational.

And, I'm lying about the ballast (sort of). I'll have concrete ballast distributed at the 4 corners and the bow to create "inertial resistance to roll", but only 125 lbs. total in movable lugs. Obviously, too many sleepless nights have added too many variables to this hull to seriously try to experiment with--but it's a cheap hobby in the size I'm talking about...
 
#12 ·
Regarding heeling and the sides/chines/skegs/twin-keels "losing efficiency": That's a good consideration, and one that I have fully considered. First, all keels lose efficiency by tilting away from vertical when heeled (except twin or bilge keels). In my model these show up as vertical and they would slightly shorten in lateral resistance. The windward side/chine would come out of the water but the leeward would go deeper. Also, the "real" version will have 20 degree outward tilt and therefore they'd be getting both deeper and more vertical when heeled. Second, while they are "short" and "shoal draft" style keels or twin keels, they have extra lateral resistance due to "area". Interestingly, calculations of keel efficiency show that the leading edges are more effective than trailing, so a long keel would be inefficient by some unknown (unless you're a hydrodynamics engineer) percent. Yet sheer quantity can compensate. Third, that "quantity" compensation actually adds to wetted surface, true, yet calculations of drag from wetted surface are "inconsistent" between engineers. So I opt to just try it out in the real world. Fourth, "fast tacking" is impinged upon by all long keels and these are probably extra "good" for tracking (and therefore bad for tacking). But enlarged rudders have been documented as ways to force tacking in such "good tracking" hulls configurations. Again, trials in the real world will provide answers. I actually expect to trim and shape the length and depth of these "sides" until they permit fast tacking.

My goal for this small boat, besides being an experiment in hull design, is to "support" large sails that need plenty of "work" to handle, thus creating a "training vessel" to teach crews how to coordinate their trimming tasks with a skipper who is calculating course and wind direction. I have a narrow stretch of river behind a dam near my house and only a very small boat can be used--so I'm packing as much training into a single dinghy/skiff sized shoal-draft, non-ballasted sailboat as possible. Uh, I'm afraid to admit that this will also be tested in a schooner variant, with two masts and both jib and staysail up front on a bowsprit. Yeah, it's a crazy experiment--but it might actually work. At least it will be educational.

And, I'm lying about the ballast (sort of). I'll have concrete ballast distributed at the 4 corners and the bow to create "inertial resistance to roll", but only 125 lbs. total in movable lugs. Obviously, too many sleepless nights have added too many variables to this hull to seriously try to experiment with--but it's a cheap hobby in the size I'm talking about...
With all due respect, I am not trying to rain on your parade, but reading you posts, it would appear that you have a a minimal understanding of how keel hydrodynamics work. In an ideal world you want a keel which has minimal drag and maximum lift. You are describing a keel that has just the opposite.

While this may sound counter-intuitive, the more sail area per displacement that you put on a boat the less drag and the more lift that is needed, because as a boat becomes increasingly 'over canvased' the side forces increase proportionately, and to avoid excessive heel angles, that side force needs to be partially absorbed by acceleration. Drag prevents that acceleration. This becomes very obvious in gusty conditions where you will find a boat much more likely to heel more in a gust if the bottom is fouled.

The longer the keel, the more critical the attack angle of the keel becomes with heel to minimizing drag. With heel the angle of the centerline of the boat changes relative to its direction through the water. As you move further from the centerlne that change in angle is exaggerated by the water flow. Because of this, the angle of the actual direction of water flow over keel mounted near the chine will vary very widely as well. This is not so bad on a short chord foil like one of Bolger's leeboards, but it produces a huge amounts of drag on a short shallow keel.

Jeff
 
#11 · (Edited)
Assuming my orientation is correct and I labeled the model as I think it should be below...

What you have built is a very poor performing trimaran. And needs to be analyzed that way. What I have labeled a 'lateral fin' is really just a very, very low volume ama. Which means lots of drag for very little gain. It will add a reasonable amount of lateral resistance to leeway, but at the cost of huge drag increases from the skin friction, wave making resistance, and surface piercing drag. The boat will always want to turn to leeward thanks to this drag, which means more rudder input, which means more drag.

It's a vicious cycle, and will result in a very poor performing boat.

Worse, if you ever heel enough that the wings hit the water, expect to come to an abrupt and somewhat violently stop. I have sailed on two boats that used wings and in both cases the wing hitting the water was quickly followed by the driver being yelled at by the foredeck to get out of his space.

Adding lifting foils to the bottom of this wing isn't going to help much, they will be relatively low aspect, which means lots of drag, minimal lift, and did I mention lots of drag?

Compare this to a high volume trimaran, where as it heels over the float immerses and provides massive amounts of buoyancy, the drag is evenly distributed for and aft of the boats maximum rocker to minimize turning momentum and the extra drag is tolerated for the increased RM and decreased weight. They also allow for a smaller central hull since the amas can carry the buoyancy helping to reduce drag.


Moving weight to the four corners is probably the absolute worst thing you could do in terms of performance under sail. It may make a raft more stable, but once a boat I sail underway things change. You want weight centered, low and directly over the max rocker. Which is why all trimarans try to minimize storage in the amas and move it all to the main hull.
 

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#14 ·
Thanks, Stumble. Good points. I agree that this resembles (but not in a good way) a trimaran. I actually started with outriggers as the initial concept.

Yet the reasonable and theoretical drawbacks you point out have never actually been tested in the way I propose testing. Taking each point in turn:
- the lateral fin or side extension, when sized and placed optimally, will hopefully be less resistance than an outrigger, though functionally identical
- the side keel will be central to the displaced area when heeled and thus not induce any turning moment, which is countered by the long straight keel shape anyway
- the wings/fins/foils side extensions will always be immersed partly and never suddenly hit; though the drag you mention may or may not be greater than the extra sail area can compensate for--we'll see
- also, this is not a skimming racing surfboard flying at high speeds; it's a displacement hull aiming for 5-ish knots maximum, if lucky
- the RM of my lateral fins may be nil, at these speeds; so an outrigger may in fact be the only solution for shoal draft. This really is just a scow sailboat with draggy leeboards, in the end. I'm wondering if lift can be better than ballast for RM at these speeds... doubtful, I admit.
- the "distributed" ballast concept is purely for stability, actually for comfort and anti-shaking inertia. This is one of the least documented or tested concepts for small keelboats. Ted Brewer's comfort ratio shows zero recognition that displacement weight in the skin and superstructure vastly changes the motion experienced by crew from waves and gusts. Ballasted deep keels do in fact help with roll but not at all with pitching.
- performance, per se, is the least documented aspect of twin keels, I've noticed. Everyone knows turtle-like twin keels in England but those same hulls, rigging and displacements would have been equally horrible with fin keels. Experienced hull engineers "talk" about wetted surface drag and compensating for it with sail area (often together with low aspect rigging), but I've written these engineers directly and they've never built a boat themselves to test it.

So my reason for posting this question--since I'm going to build a small toy anyway to start testing these nutty ideas--is to find out if anyone knows of anyone who has actually built similar things. I expect the actual dimensions of my scheme will make the difference between fantastic performance and sinking like a rock. But I can get out my skill saw and chop off pieces and change fin shapes and adjust ballast/displacement ratios rapidly once I get a baseline performance analysis completed.

What started this experiment was noticing that "barge" (square) shapes are rare and no designers could tell me why. Ugliness, was one designer's suggestion. But the "rocker" in most hulls was actually spoken of as a problem that they needed to compensate for, yet they wouldn't just eliminate rocker in a test model. I suggested that strength during collisions as a reason for rounded hulls, but the engineers noted that the rigidity of rounded hulls actually makes puncture more probable. The gentle deadrise others advocate could actually be provided by a flat, shoal draft hull design.

Of course, I'm actually expecting that there is no way my tests will succeed; but I'd like to have actual results. I could just make a pdracer (puddle duck) and race it with the one-design class of dinghies and save myself, uh, all the fun of dreaming up stupid hull shapes...
 
#20 ·
Thanks, Stumble. Good points. I agree that this resembles (but not in a good way) a trimaran. I actually started with outriggers as the initial concept.

Yet the reasonable and theoretical drawbacks you point out have never actually been tested in the way I propose testing. Taking each point in turn: thats because 5000 years of naval architecture indicates it won't work for a whole host of reasons.
- the lateral fin or side extension, when sized and placed optimally, will hopefully be less resistance than an outrigger, though functionally identicalthere is no optimal place for it, it's the wrong shape. The fin will provide some but not much lateral resistance, but lots of drag. This is very well understood, low aspect foils generate a lot of drag for each unit of lift.
- the side keel will be central to the displaced area when heeled and thus not induce any turning moment, which is countered by the long straight keel shape anywayit needs to be centered on the CE not CB.
- the wings/fins/foils side extensions will always be immersed partly and never suddenly hit; though the drag you mention may or may not be greater than the extra sail area can compensate for--we'll seei am talking about the wings. When the crossbeams hit they will suddenly stop the boat. The lateral foils are going to generate lots of drag, a little lift, and minimal RM. This is litterly the opposite of what you want from both a foil and an ama.
- also, this is not a skimming racing surfboard flying at high speeds; it's a displacement hull aiming for 5-ish knots maximum, if luckyit takes just a step much work if not more to build a slow boat a size a fast one.
- the RM of my lateral fins may be nil, at these speeds; so an outrigger may in fact be the only solution for shoal draft. This really is just a scow sailboat with draggy leeboards, in the end. I'm wondering if lift can be better than ballast for RM at these speeds... doubtful, I admit.agreed.
- the "distributed" ballast concept is purely for stability, actually for comfort and anti-shaking inertia. This is one of the least documented or tested concepts for small keelboats. Ted Brewer's comfort ratio shows zero recognition that displacement weight in the skin and superstructure vastly changes the motion experienced by crew from waves and gusts. Ballasted deep keels do in fact help with roll but not at all with pitching.Your kidding right? Getting weight out of the ends is one of the best understood parts of boat design. Ask any racer, even without a technical background and they will tell you to get weight out of the ends. It kills boat speed, it robs the boat of momentum... it really is one of the first rules of yacht design.

The comfort ratio was generated as a joke, and taking it more seriously than it was intended is a mistake. It grossly favors heavy very narrow boats, because apparently sailing at 30 degree heel all the time is comfortable.
- performance, per se, is the least documented aspect of twin keels, I've noticed. Everyone knows turtle-like twin keels in England but those same hulls, rigging and displacements would have been equally horrible with fin keels. Experienced hull engineers "talk" about wetted surface drag and compensating for it with sail area (often together with low aspect rigging), but I've written these engineers directly and they've never built a boat themselves to test it. you mean other than all the high performance twin keel boat? Like the RM. There are some real advantages to twin keels, like being able to dry out in a tidal estuary, and shallower draft, but they are not a performance upgrade. The added wetted surface combined with the lower RM for the same ballast means a boat that is always slightly slower and carries more heel than the same hull wi a normal keel. This can be mitigated via good design, but there is a limit to how far it can be pushed.

So my reason for posting this question--since I'm going to build a small toy anyway to start testing these nutty ideas--is to find out if anyone knows of anyone who has actually built similar things. I expect the actual dimensions of my scheme will make the difference between fantastic performance and sinking like a rock. But I can get out my skill saw and chop off pieces and change fin shapes and adjust ballast/displacement ratios rapidly once I get a baseline performance analysis completed. i doubt it.

What started this experiment was noticing that "barge" (square) shapes are rare and no designers could tell me why. Ugliness, was one designer's suggestion. But the "rocker" in most hulls was actually spoken of as a problem that they needed to compensate for, yet they wouldn't just eliminate rocker in a test model. I suggested that strength during collisions as a reason for rounded hulls, but the engineers noted that the rigidity of rounded hulls actually makes puncture more probable. The gentle deadrise others advocate could actually be provided by a flat, shoal draft hull design. take a look at the Mini 640 fleet where scow bows are coming back into vogue. This type of bow I sail good off the wind but the high entry angle means a lot of slamming going upwind (The mini's generally only race downwind). Barge hull shapes are very well understood, they just have major limitations. But these tradeoffs are not some unexplored area of naval architecture, they just don't work very well for most sailboats.

Of course, I'm actually expecting that there is no way my tests will succeed; but I'd like to have actual results. I could just make a pdracer (puddle duck) and race it with the one-design class of dinghies and save myself, uh, all the fun of dreaming up stupid hull shapes...
I agree with your prediction. This thing is going to be slow, point badly, have minimal load carrying capability, be very sticky in light air, trip over itself in heavy air, and have a lot of leeway. But if you do a decent weight study it might float on it's lines.
 
#16 ·
Thanks, Jeff.
I agree that I am questioning and planning on testing something that the theories say has serious hydrodynamic flaws. It's the percentage impact of those negative side effects versus potential for compensatory benefits that I want to test.

My impetus is that a friend has a half built 100 ft aluminum bilge keel, over-canvassed, low-aspect yacht that the theories say will be a dog. Yet the highly paid designer says it ought to average 13+ knots over the open ocean (though he has never had one built). My dinghy faces equal theoretical challenges.

My need is to have a small boat that is hard to sail. By "hard" I mean one that requires several crew members to do on a small scale everything a schooner requires on a large scale. My challenge to myself was to see how small I could go and still hold 3-4 crewmembers all trimming sails and navigating in confined waterways. It's intended to be a training vessel, nothing else.

And I value the debate and really appreciate everyone's time--though I can see that I appear to be a stubborn land-lubber... (I am, actually, despite growing up sailing daily every summer.)
 
#17 ·
You got that quote right, Capta. Undue weight in the ends of any vessel bodes ill in blue water, I expect. I'm only planning on fighting the bounce when crossing wakes of power boats. Oh, I I want to emulate the feel of a big, heavy boat, to slow the responsiveness to tiller activity and sheeting in and out. Hmm. I guess that means I'm trying to degrade performance...
 
#19 ·
Looking forward to seeing how this goes. There are always things learned in doing, rather than just applying theory. I have only built a couple of tenders for the big boat. They have both taught me (mostly unintended) lessons in materials, stability, etc.

Post some drawings.
 
#22 ·
Thanks, Jeff.

Taking my foot out of my mouth, I confess to making many sweeping statements while thinking about the tiny "scope" of people creating very tiny dinghies or even less than 20 ft displacement boats intended to model "cruising" sailing conditions. When I say people aren't testing things, I'm referring to people actually building twin or bilge keel boats intended for maximum cruising performance. This lack of real world boats created specifically to test just that feature is why "everyone" says that twin keels are slow, don't point, can't tack, and slip leeward excessively. The computer models and just plain insightful "thinkers" out there can and have thought of many ways to avoid those problems. But they haven't built boats to demonstrate their solutions.

Thanks for confirming my suspicions on scows that heel over. As you said, I thought scows became sharpies when heeled and balanced just right. Though I think these tend to be trapeze-equipped racing vessels in most examples I've seen.

Also, M-shaped hulls are technically a smoothed out variation on placement of foils or dynamic righting moment devices--and they maximize wetted surface double the amount of a flat or barge hull. The need for speed, as you say, makes incorporating M hulls or foils in any slow sailing scow a challenge. But I've not found anyone who has actually tested the net drag of all this wetted surface on a balanced small boat with enough sail area to overpower it. You did use the four-letter word "gust", which might explain why this is a dead end, I'll concede. A balanced boat at speed under unwavering wind with dynamic righting moments finely tuned could just flip over in a heartbeat when hit by a gust. Sort of like releasing a rubber band from your finger pistol...

And, again, thanks for correcting my absurd blanket statement about wetted surface and rocker "research". I only meant studying them when applied to tiny sailing dinghies operating in displacement "mode". By that, I mean carrying 1000 lbs in a rowboat. And I meant "tests" confirming any computer models in this small scale. I've tried to find if anyone has raced a flattened pdracer without the rocker and ballasted against heel so that it could carry double or triple the sale area. So, I'll just invest a little effort and test it myself.

And regarding that 100' schooner's average speed of 13 knots in a crossing. The designer says it should hit nearly 20 knots in optimal (high) winds and cruise steadily at 18 knots with diesel assisted sails during 15 knot winds. But it isn't finished yet...

Thanks again, Jeff, for rebutting my oversimplified generalizations. If you only knew the ones that I had already edited out of my text, you'd see how much hot air I'm capable of.

I probably will provoke similar rebuttals every six months, since I'm going to be building and testing progressively larger vessels. This time my "success" standard will be to make a dinghy that can carry 4 people while teaching them how to sail with the "feel" of the boat being similar to a much larger one. The intention is to make this dinghy a schooner (after phase one tests are finished) with gaff rigged sails and both a jib and staysail off a bowsprit. I need lots of lines for trainees to mess with and frequent course changes to tire them out.

Thanks again,
Phil
 
#23 ·
Consider a 20'gaff ketch rig on a dory bow, skiff stern near flat bottom hull with a lee board on a lanyard. Wedges on the lee board set the angle from centreline and vertical when heeled. Pretty standard appearance. point cheatingly well, keeps crewhands busy and easy to build. Not a new kind of wheel but worked for me.
 
#24 ·
Thanks again for thought provoking comments from all.

Update:

The basic prototype will be more or less the same as described, but probably will have a moderately inverted V hull and a different bow. This reduces wetted surface, but I mostly want to test out leeway of the twin skeg/keel hull while also playing with Sea Sled features. If I were a "real" engineer I'd never test two weird things at once. But I can remove the inverted V later if necessary, since it will just be three plywood pieces added to my former design in its scow version (rather than sharpie).

I might throw together an inverted V canoe first, in any case. I have a normal canoe and a catamaran-ish kayak already. I can measure stability by building a prototype sailing canoe in a weekend. My sailing dinghy will probably take 6 or 8 weekends...
 
#25 ·
If your experiment is solely about stability, you can draw up the sectional shape of two simple hull forms, one with the vee and a control of what ever shaped hull form you want to use, setting the water line at equal displacement levels. Then rotate the hulls through the same angles and immersion and calculate the stability at each angle. If you set up a spreadsheet, you can do these calculation very accurately in a few hours and the software can plot them in a couple hours.

Pick up any yacht design text and you can find the formulas.

That should be way cheaper and more accurate than any test that you can do with a full size boat.

Jeff
 
#26 ·
Yes, I've done that (regarding stability calculations under differing degrees of heel).. The inverted V shows greater static righting force and greater stability. My interest, however, is not in each single feature's calculated outcome, but in all of them put together with the goal of how it "feels" to sail it. Shoal draft feels stiff up to a point and under limited winds, but how quickly the helm or sheets can be trimmed under gusts or heavy weather and whether the design is "good enough" can only be tested. And a few weekends of hobby boat building is a very small cost after the calculations have provided all their data.

One aspect of the opinions that float around out there regarding hull shapes is that most experimental hulls are tested under motor power in fast boats. Trolling speeds aren't of interest to lots of the researchers... Well, the tugboat and barge researchers do provide interesting data that could apply to sailboats, but they have much more mass involved...

It's interesting to me, how many of the ideas I'm interested in came from advertisements for various products, from emergency lifeboats and tenders to high speed runabouts to barges to racing catamarans. Each of those ideas had already been tested in R&D and put into someone's production line and marketed. For example, on e folding dinghy ad contained a link to another competitor with a unique hull, which mentioned how "wet" the ride was, which led to other ads for boats that were surprisingly "dry". Hence my prototype's use of hanging the cockpit bench outside of the hull with combines extra dynamic righting force along with suppression of spray.

I may nevertheless discover the wettest and tippiest sailing dinghy form factor...

Regards,
Phil
 
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