Wide Transoms...A Discussion Thereon. (was Jeff-H) - Page 2 - SailNet Community
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post #11 of 29 Old 01-04-2005
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Jeff-H

My take on all this is simply a wide transom on a displacement hull that does not come out of the hole does nothing to improve seaworthiness and would also hurt you in following seas.Actually with that setup you would slow down. In a design which promotes planing,it helps raise it out and if you are racing that is where you want to be.Now if seas are getting heavy and you need to reduce speed and thus loose the ability to plane I look at it being a disibility in a following sea. anyone else agree?
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post #12 of 29 Old 01-05-2005
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Jeff-H

Jeff When I read 12 to 20 I didn`t realize that it was meters! What you are describing is a mountain of water.I live in the North Atlantic where some of these exist but if ever hit with one I wouldn`t be writing about it after sailing in a 30 foot boat.It wouldn`t matter if my transom was 2 feet wide or 20 feet wide.I`m sure the other posts are trying to make the point of a 12 to 20 foot sea.And before someone writes in and says they did ,where there is 1'' 20 meter wave there will be more to follow and in the boats we are describing here, if you ever did survive such an event you must be living a church going lifestyle.
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post #13 of 29 Old 01-05-2005
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Jeff-H

What is ideal for racing, is usually not ideal for cruising and even for ocean racing, wide hulls and transoms make only sense if you are limited by the rules and can not have a longer and less beamier boat, for the same weight..

Listen what Dave Gerr says about that:

"Wide, shallow hulls tend to pound upwind (and sometimes downwind). They can be difficult to steer because when they heel, the waterplane becomes far more asymmetrical than a narrow hull of the same parent form.

....The ultimate drawback of wide, shallow hulls is that their reserve stability is usually very poor.

Generally, a moderately slender hull (longer for the same displacement with a careful thought-out waterplane moment of inertia and a low enough vertical center of gravity ) will be a better all-around performer than a wide shallow hull.

The moderately slender hull will also be easier to manage and more confortable in a seaway."

Dave Gerr in an article published in Sail Magazine - 9/2004.


I think that cruiser/racers or racers are beamier and have larger transoms because they have to maximize initial stability (sail power) to a given length.

I think that passage makers are not designed thinking in racing, they donít have to maximize performance for a given length, they are designed thinking in seawordiness and overall performance and thatís why they are less beamier and have more moderate transoms.


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post #14 of 29 Old 01-05-2005
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Jeff-H

I basically agree with Dave Gerr that "Wide shallow hulls tend to pound upwind", but we are not discussing wide, shallow hulls. We are discussing moderate beam boats, which have had their center of buoyancy moved aft, resulting in comparatively wide transoms. More specifically these are precisely the boats that Dave Gerr is referring to when he says, "a moderately slender hull (longer for the same displacement with a careful thought-out waterplane moment of inertia and a low enough vertical center of gravity) will be a better all-around performer than a wide shallow hull. The moderately slender hull will also be easier to manage and more comfortable in a seaway"

The idea that racers and racer/cruisers are by definition "beamier and have larger transoms because they have to maximize initial stability (sail power) to a given length" is very much an outdated idea, at least in terms of the IMS derived performance cruising boats upon which my comments within this discussion are based.

Respectfully,
Jeff



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post #15 of 29 Old 01-05-2005
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Jeff-H

Again, I have a problem with using anecdotal data on a small sampling to make a case. I have sailed traditional 26 footers that tracked well in a wide range of conditions (my folkboat for example), and a whole bunch of equally narrow traditional boats that tracked miserably. I am not sure what kind of boat that you own so it is hard for me to comment. I also want to point out that I have been agreeing that there is nothing worse than a poorly designed boat with a a lot of beam that results in wide transom and you may be unfortunate to own one of them.

But the original question was about boats with large transoms and how could they possibly handle well. It was not about about beamy boats that also had wide transoms.

Gerr says "moderately slender hull", he does not say extremely narrow. 9''8" beam on a 60 footer is extremely narrow. perhaps using a couple example to explain my point, I think that we would all agree that a late 1990''s era Hallberg Rassy 39 with a 12''-4" beam has a moderately narrow beam and a small transom. In comparison, the 40 foot Beneteau 40.7 which is at the racer and beamier end of the spectrum that I am speaking of, has a beam of 12''3. Similar beams. The 40.7 actually has a narrower beam to waterline length than the Hallberg, yet the Beneteau 40.7 has a much wider transom. Based on a conversation with an owner of a Hallberg Rassy 39 who delivered a 40.7 in heavy conditions, he felt that despite the short chord foils on the Beneteau, the 40.7 was easier to keep on course in a following sea.

While you are right that in a following sea, the water has a larger area to lift on a boat with a wider transom, the more aftward position of the center of gravity on a properly designed large transom boat means that there would not necessarily be a change in trim, and the finer bow would trick the water into thinking that this is a narrower boat helping the boat to track better, than a boat that has a fuller bow.

Respectfully,
Jeff
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post #16 of 29 Old 01-06-2005
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Jeff-H

I think that we have gotten to the point where we are perhaps debating semantics rather than substance. I understood that the reference to the 9''8" beam 60 footer was quoted from Gerr and but I also understood that he referred to that beam to length ratio as ''extreme''. In the quote he contrasted the beam to length ratio of the Open Class 60 with a moderately slender beam that he says is more ideal for cruising. This dovetails with his other quote extolling the virtues of a well modeled moderate beam boat, which I still contend is precisely the boats that I am also advocating. The clue to that we are talking about the same thing his discription suggesting the importance of carefully modeling the waterplane shape of the boat.

I think that Gerr is saying that from his stand point the perfect racing hull is an extremely slender hull but that the perfect cruising hull is moderately slender. He and I are agreeing. What is not explicitly being discussed in Gerr''s quote is the longitudinal position of the center of gravity and buoyancy. The current thinking on seaworthy and seakindly design principles places the center of gravity and center of buoyancy further aft than they had been in the past. This results in larger stern sections than had been typical in 20th century designs.

With regard to the choice of boats to compare, I purposely chose the Hallberg Rassy 39 specifically because it is an older and highly respected offshore design. I chose this example trying to illustrate that these newer designs with larger transoms do not have to have to have an extreme beam in order to end up with larger transoms and that the transom size resulted from the aftward placement of the maximum beam rather than from an increase in overall beam of the vessel as been suggested in early discussion.

Lastly like so many things in yacht design, I am a firm believer in moderation in the design process. While extreme design may be justified for all kinds of very spicific applications, when designing a cruising yacht I feel that there is a need moderation in all of design decisions that a designer may consider. I believe that I am in agreement Dave Gerr and with the majority in this discussion that is not a healthy thing to carry to any extreme such key seakeeping factors as the amount of beam, overall displacement, transom size and shape, the distribution of weight and buoyancy, or the position of center of buoyancy and gravity, etc.

I think that we are now discussing the finepoints of our individual definitions of ''extreme''and I am trying to point out that within this discussion there is a range of transom size and weight distribution that may not coincide with historic norms but within any reasonable definition are still quite moderate and when incorporated with properly integrated and balanced design has been shown to successfully improve seakindliness, seaworthiness, load carrying capacity, and performance over more traditional hull forms which were conceived within the limitations of the materials available and the specific uses for which these vessels were being used.

Respectfully,
Jeff
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post #17 of 29 Old 01-06-2005
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Jeff-H

This time I have to say that I agree with you.
It is clear that in recent boats, even in passage makers, designers have also"place(d) the center of gravity and center of buoyancy further aft than they had been in the past. This results in larger stern sections than had been typical in 20th century designs".

But you do not need to have large transoms to do that. Large transoms that offer more surface to breaking waves are not a desirable thing in itself.

To see what I mean, go to the Malo site and take a look at the new Malo 40. Compared with the 10- year-old 39, it has larger stern sections. That, in the less expensive version results in a slightly broader transom, but in the Classical version (that, I think is the one that goes with the spirit of the boat) the narrow transom is maintained.

Being the waterplane the same in the two versions, they have similar sailing characteristics.

The Classic version has the added advantage offered by the small transom in following heavy seas.

Of course, it has also two disadvantages: the small increase in weight (that I don''t believe it has any importance in this type of boat) and the increase in price.


Respectfully


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post #18 of 29 Old 01-06-2005
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Jeff-H

Jeff, I admire your patience. As an owner of a very beamy cruising tub, with a moderately fat ass, that, little known to most, has racing pedigree ( hull designed by Nelson Marek) I can attest that the long, but relatively light nose is easily controlled, even when running downhill.

If waves become 12-20 meters, it doesn''t matter what you''re driving, you throw a drogue out the back and slow down, or else you run the risk of digging in the bow, fat, skinny or indifferent.

For a good visual:

http://www.woodenshoemusic.com/Images/familypics/Forumshots/TopClimber.jpg

Oscar
C42 # 76 "Lady Kay" (Ex. C250 WB #618 )
Georgetown MD/Fort Lauderdale FL
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post #19 of 29 Old 01-06-2005
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Jeff-H

Whatever patience I have comes from years of light air sailing and trying to explain and reach understandings about complex subjects over a medium that really is pretty ill-suited for that purpose.

While I basically agree with you about trailing a drogue in those conditions, I once talked to a fellow who single-handed a sistership to my boat from Capetown, SA to the Carribbean. He told me that he was in 30 to 50 knot winds for the first 10 days and was sailing in seas that built to what he estimated to be 40-50 feet in height (trough to crest)with occasional higher waves thrown in. He said he ran for days under just a jib or a storm jib with the windvane doing all of the steering. He said that he was at 16 knots long enough for that to show up on his GPS as his fastest speed run. I only mention that because no one would consider my boat to have a small transom, but she is not terribly beamy either. The newer designs have even better seakeeping and tracking ability than my boat which is more than a 20 year old design.

I do want to repeat my earlier comment that designing a boat with a largish transom and good seakeeping ability takes a lot more care in modeling than designing a boat with its center of buoyancy further forward and a narrower run. Done right, it is worth the effort. Modeled poorly, the boat can be a real handful.

Regards
Jeff
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post #20 of 29 Old 01-06-2005
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Jeff-H

Jeff did you ask this guy if he was crazy.50 foot wave ,surfing at over 16 knots!Sure he wasn`t on an episode of fear factor.Not to mention days of this activity.This is definitely scaring off wannabee sailors.This guy actually went to sleep.Now that sounds like a real family outing.
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