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Go Back   SailNet Community > On Board > Boat Review and Purchase Forum > Sailboat Design and Construction > The ratios and other numbers - can someone enlighten me or point me to a resource?
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Thread: The ratios and other numbers - can someone enlighten me or point me to a resource? Reply to Thread
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Topic Review (Newest First)
07-08-2008 08:49 PM
arbarnhart Jeff,

I think you nailed my primary concern - big water. Based on mostly anecdotal evidence, I think it handles wind pretty well in terms of not getting completely knocked all the way over before recovering (if that's what you call depowering and heading up). I have only been in touch with one person who has ever taken one into true blue water and he doesn't recommend it for such. A few others sail off the coast but stay near shore. Oddly, I still have not encountered a roll over story. Maybe there just aren't that many of the boats or most are sailed in protected waters; I don't know.

Again, I don't plan to do blue water. But I wouldn't want to set out on the Beaufort to Lookout run if I thought that a squall that produced big breaking seas would almost guarantee a roll over. If I thought it might but that if I sailed well I would be okay, then I would be okay with choosing to take that slight risk (assuming the chance of bad weather was low to begin with). The run I am talking about is about 7 miles of exposed sailing near shore. If there were big crashing waves, shore wouldn't exactly be a safe haven though. And yes, I know what they call this part of the Atlantic...

"Near disaster zone"? That's a pretty harsh rating. Would it be worthwhile to secure more weight in the bilge or is that just rearranging the deck chairs?

Thanks for the frank assessment.
07-08-2008 04:59 PM
Jeff_H I would suggest that almost all of those number have zero or no bearing on the reality at hand. Newport, and most trailer-sailer builders of that era routinely published displacements that were way low of the actual weight of the boats. These published weights were typically based on pretty hypothetical dry design weights, which made no consideration of actual sailing weights, let alone crew weight. Published sail areas were typically with the stock overlappinbg headsails, and were not with 100% foretriangle as is supposed to be used for SA/D and so your SA/D is probably substantially lower than you think as well. Motion comfort is probably about right for a boat with relatively hard chines and a flat bottom, a high vertical center of gravity and so on. Then there is Capsize Screen Formula, which is mostly a useless formula since it does not include the major factors that control capsize (vertical center of gravity and buoyancy, dampening etc.). That said with the Newports high vertical center of gravity and low ballast ratio they should be in the near disaster zone of 3 or 4.

Having sailed trailerables out in the Atlantic Ocean shoals, it comes down to this, in good weather you should be fine, but when things turn, and they can quickly, you can get very steep, very tall waves, and a boat like this is easily rolled.

I once did an offshore race out of Savannah on a 25 IOR quarter tonner that I owned where we needed to round a mark roughly 5 miles offshore. The weather was predicted to be nice and the race began just that way. As we rounded the mark teh weather turned really nasty, and within 15-20 minutes we were in 10-12 foot seas that were occasionally breaking and threatening to roll us. This was a boat with a 40% ballast ratio and 5' 6" draft. The Newport is a boat with a 23% ballast ratio when dry, and far less loaded.

Jeff
07-08-2008 04:55 PM
arbarnhart I don't think so, but it does warrant a closer look just to be sure. I have a cutting diagram of the keel itself (PO had a new one made and gave me the diagram in case it ever needs another). and there is no hole in the keel itself for a through bolt other than the swivel point and the cable eye.
07-08-2008 04:16 PM
sailaway21 barney,
My Cal has a hole located near the pivot point for the keel for the insertion of a locking pin. I assume there are no unexplained and unused mystery holes in the forward end of your keel trunk?
07-08-2008 03:54 PM
arbarnhart I crewed on a friend's QuickStep 21 last October for a Beaufort to Lookout weekend trip that I am contemplating doing in mine this year. It would have been no problem. Could have done it in a Sunfish; the weather was perfect! But I have read trip reports from other outings on that same route that started that way and turned nasty. If weather like that was likely I wouldn't go at all. If it was reasonably possible but not highly likely, I might make the drive down and decide at the ramp between the outside route, the back way (a narrow channel with a lot of traffic) or not going. I would not purposefully decide to go out into high winds and big waves, but I want to be prepared for the possibility of it occassionally happening.
07-08-2008 02:57 PM
johnshasteen Those capsize numbers have a bit more meaning to boats that are actually capable of (or contemplating, or dreaming of or wondering if they are capable of) venturing afar offshore and realistically anticipating heavy weather that they cannot outrun - a category into which your boat does not fit. What it is, is a great trailer/sailer built for the nearest lake or bay - just enjoy it for what the manufacturer says it is "...makes it a good boat for novices at sailing". Could you take it across the Gulf Stream, sure, you could go in a sailing dinghy - with a lot of sailing skills, a modicum of luck and no bad weather.
When you're ready for offshore sailing there are a number of small boats that can serve you well - however, many of them are not trailerable.
07-08-2008 01:36 PM
arbarnhart Sway,

I am disappointed in the calculations, not the boat. I probably should have placed a rolleyes up there, but I didn't (and don't) want to imply that they are totally useless; they just don't seem to be geared toward evaluating this type of boat. I was hoping they might give me some insight but some of them grossly conflict what I know about the boat from experience. It will plane as well as surf so I knew that number was not a big deal. Some N17 owners beef up the motor bracket and go with a light outboard in the 10HP range to make them somewhat like a smaller version of a boat that gets a rather MiXed reception around here. The PO told me he was just getting it on plane with a Honda 5 (which I did not buy as he wanted as much for it as the boat) and I have not had a chance to try my old-but-new-to-me Sea King 5 yet, which is (hopefully) one of my improvements.

I have roller reefing.

I am planning to add one or two cockpit drains out the transom. One of the few design decisions I don't like is that the cockpit only drains through one hole near the companionway into the keel trunk. Besides the possibility of slow draining if pooped, it is a pain at the car wash - it is not the low point when it is on the trailer attached to the car. Another N17 owner put an inspection hatch in the cockpit floor at the transom which he opens at the car wash and lets it drain out the bilge and some have added transom drains. I am planning to add at least one drain back there.

I also plan to add some D rings so I can lash things down. Floating things don't displace water very well.

My hatch can be closed and secured, though the current arrangement can only be well sealed from outside and not opened from inside when sealed. I am planning to make a door for it that slips in as a one piece hatch board. The current one is a two piece.

I would really like to come up with something for a keel lock. I have heard that mentioned before. Ideally, it should be quickly/easily engaged/disengaged so as not to lose the ability to haul it up quickly if I get in too shallow.

Thanks for the encouraging words. For a lot of reasons, a bigger boat just isn't in the picture in the near future. I am so darn good at justification I have to run around asking people to poke holes in my plans for me though.
07-08-2008 11:22 AM
sailaway21 arbarnhart,
I think you're being much too hard on your Newport 17.

I disagree completely with the hard to sail conclusion. In fact, I think the boat is easily single-handed as well as being blissfully uncomplicated for any inexperienced crew you may have.

The low displacement to length ratio, and the resultant conclusion of a bad ride and difficult to sail is a generalization that may not apply either to your sailing area or your boat. If you're out in the heavy stuff she'll not ride as well as some other boats of differeing hull forms, displacement, or length. On the other hand, she's easily sailed solo and you need only the lightest of air to get her moving. While other "more seaworthy" boats are essentially becalmed you'll be sailing right along. While your hull speed is lower, you'll achieve it much more easily and in much lighter air. In fact, you'll be reefing in conditions that heavier boats just get moving in! You'll also find that your boat is far more nimble than many others; she'll respond quicker and accelerate quicker.

As to your capsize number and heavier seas. You'll want to make sure that you can secure your keel in the lowered position in the event of a severe knockdown and potential roll over. You really don't want it slamming back up into the keel trunk and you certainly want to preserve your righting moment in such a circumstance.

You can do something about your ability to avoid capsize as well. If you do not have a reefing system, install one. Can your companionway hatch be closed and secured? What do you have for washboards? consideration might be given to increasing the size of your cockpit scuppers and drain lines. And when venturing out you can reduce the volume of your cockpit, which will decrease that capsize number, by filling it with stowed and secured gear. That big ice chest you may want to carry will take up a significant volume of cockpit space and that is space that water cannot fill when in a capsize situation.

And you may well see six knots. Chances are it will be downwind and surfing!
07-08-2008 10:48 AM
arbarnhart One last follow up - I used the comparison chart feature on the site and compared it to a Monty 17, WWP 19 and Seaward Fox and they fared pretty similarly (actually capsize ratios were slightly higher for some reason).

I am still not sure about the self righting question. It seems to my simple mind that it is a case by case design question. I can duct tape a nickle on a clorox bottle and make it self righting.

The biggest things I plan to do are the outside run from Beaufort to Lookout (very near shore about 7 miles between the inlets) and possibly an Ocracoke trip (crossing part of Pamlico Sound).

http://www.ncdot.org/it/img/graphics/boatguide/10.gif

http://www.ncdot.org/it/img/graphics/boatguide/8.gif
07-08-2008 10:26 AM
arbarnhart
Quote:
Originally Posted by T37Chef View Post
Thanks - I did (pasted in below).

I am going to be uncomfortable in motion, probably hard to sail, capsize easily and never go 6 knots. I get the impression that the calculations aren't really made for small boats.


boatName=Newport 17
LOA=17.75
LWL=16.1666
beam=6.3333
displacement=1000
sailArea=147

displacementToLWL=106
Displacement to LWL: A medium value would be 200. 300 would be high (Heavy Cruising Boat) and 100 would be low (Ultra Light Displacement-ULDB). Boats with low numbers are probably uncomfortable and difficult to sail.

speed=5.39
Calculated hull speed.

sailAreaToDisplacement=23.52
Sail Area to Displacement: The sail area is the total of the main sail and the area of the front triangle. I cannot be sure that this datum was entered correctly for each listed boat. A racing boat typically has large sail area and low displacement. A number less than 13 probably indicates that the boat is a motorsailer. High performance boats would be around 18 or higher.

LWLToBeam=2.55
LWL to Beam: A medium value would be 2.7. 3.0 would be high and 2.3 would be low

motionComfort=7.89
Motion Comfort: Range will be from 5 to 60+ with a Whitby 42 at the mid 30's. The higher the number the more comfort in a sea. This figure of merit was developed by the Yacht designer Ted Brewer and is meant to compare the motion comfort of boats of similar size and types.

capsizeRatio=2.53
Capsize Ratio: A value less than 2 is considered to be relatively good; the boat should be relatively safe in bad conditions. The higher the number above 2 the more vulnerable the boat. This is just a rough figure of merit and controversial as to its use.

category=racer
Sailing Category: The four categories are racer, racer/cruiser, cruiser/racer, and cruiser in order of descending performance

ppi=366
Pounds per Inch Immersion: The weight required to sink the yacht one inch. If the boat is in fresh water multiply the result by 0.975. If you know the beam at the waterline (BWL) multipy the result by BWL/Beam.
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