Bustle Ahead of Rudder Turbulence

[malbert73]

This a Pearson 40 (ish)
Neat boat if so, despite IOR roots. Shallow draft, nice accomodations... Tough companionway, though

[ronbo1]

Likely you'll experience no difference after labor and materials involved.
Surely you have more pressing projects on such a fine boat.

Ronbo

[malbert73]

Originally Posted by ronbo1

Likely you'll experience no difference after labor and materials involved.
Surely you have more pressing projects on such a fine boat.

Ronbo

Boooo.

Everyone needs fun projects to distract from drudgery like changing head hoses, etc.

[silverp40]

Thank you for all the kind comments...


Quote:
The angle at which the buttock lines intersect the CL is critical in the run of the boat, and yours is presently less than optimal.

Hey Minaret, can you please be a little more specific, I lost you. CL is centerline?

Yes, the vanes were just a structure on which to build the final skin. I would beea lot of fairing to fill the entire bustle with filler!

Malbert, correct, Pearson 40, different a lot from the P39 - shallow draft, heavier, more IOR I suppose since they were built about 7-8 years before the 39 came along and raced much. Companionway is steep and deep so not easy.

(I can't believe the head hose comment, I am changing one tomorrow - amazing!)

Maybe Bob Perry would find this thread....He states in his book that he did plenty of bustles in the day but do not remember which ones though.

[malbert73]

Originally Posted by silverp40

Thank you for all the kind comments...

Quote:
The angle at which the buttock lines intersect the CL is critical in the run of the boat, and yours is presently less than optimal.

Hey Minaret, can you please be a little more specific, I lost you. CL is centerline?

Yes, the vanes were just a structure on which to build the final skin. I would beea lot of fairing to fill the entire bustle with filler!

Malbert, correct, Pearson 40, different a lot from the P39 - shallow draft, heavier, more IOR I suppose since they were built about 7-8 years before the 39 came along and raced much. Companionway is steep and deep so not easy.

(I can't believe the head hose comment, I am changing one tomorrow - amazing!)

Maybe Bob Perry would find this thread....He states in his book that he did plenty of bustles in the day but do not remember which ones though.

Yes, head hoses were one of my first and least favorite jobs on my boat when I bought it. Trailing edges matter a lot, and a good taper rather than abrupt cutoff like your boat has should hep flow over rudder, which I am sure you will feel.
I faired a mere 1/2 inch off of each side of the front of my propeller aperture last winter to help reduce deadwood, and gained a lot less cavitation noise and 0.3 knts increase in cruising speed at same RPM, so I believe a lot in attached flow where possible. Like I said, your friend's boat has a much more "natural" looking shape to the skeg, trailing edge of hull.

[minaret]

Originally Posted by silverp40

Thank you for all the kind comments...


Quote:
The angle at which the buttock lines intersect the CL is critical in the run of the boat, and yours is presently less than optimal.

Hey Minaret, can you please be a little more specific, I lost you. CL is centerline?

Yes, the vanes were just a structure on which to build the final skin. I would beea lot of fairing to fill the entire bustle with filler!

Malbert, correct, Pearson 40, different a lot from the P39 - shallow draft, heavier, more IOR I suppose since they were built about 7-8 years before the 39 came along and raced much. Companionway is steep and deep so not easy.

(I can't believe the head hose comment, I am changing one tomorrow - amazing!)

Maybe Bob Perry would find this thread....He states in his book that he did plenty of bustles in the day but do not remember which ones though.

Look at the waterlines in the half-breadth view and the buttock lines in the plan view. The point at which the waterlines cross the centerline aft in in half-breadth is important here, the waterlines angle relative to CL is critical. The same is true of the buttock lines in profile, and the point at which they cross the waterline. Chappelle defined an easy run as a set of buttock lines which cross the waterline at no more than 15 degrees, something obviously not seen in modern smaller boats.

[Jim Cate]

FWIW,

One of the Herreschoffs (sp?) famously once said something like "the secret to hull design is to not surprise the water". Makes sense to me!

Good luck with your mods, which I think are worthwhile if done at a cost you find acceptable.

Cheers,

Jim

[Cheechako]

Sorry, I was thinking of the P36. Loved that boat back 'in the day"

[silverp40]

You are correct malbert, the finished look looks much more natural and I liked it when I first saw it (he just did it). The water does not get "surprised" by unnatural curves.

Insofar as the waterline angle, the faired are will be underwater, under the waterline......

Here is a shot of the back underwater profile

The P36 is usually a ketch aka 365 and good sailing, capable boat.There were hundreds built and some have crossed oceans. The sloop is relatively rare and do not see many around.

[dianaofburlingt]

I admire you for setting out to remedy this common failing on this vintage of boat. My '74 Hunter 25 has much the same issue, only slightly less egregious. That half-skeg and half-spade rudder combination is the fruit of those times and is at best a performance compromise.

When my dad designed the H25 he included a skeg much like yours, only straighter. When he followed with the Raider 33, a very similarly-shaped boat, he reduced the 'skeg' to a mere dimple. After sailing one, he concluded it should not have had such a skeg at all. It inhibits coming about and light-air performance by holding a low-pressure area alongside it, which is drag. In your case, however, the 'burble' immediately forward to that last vertical edge of the rudder is a worse source of drag. By all means clean it up; and seek the straightest line you can along the bottom of the skeg.

Professionally speaking I do not think your intended improvement is a particularly rough task at all. (I do this sort of thing all the time!) You might even consider using foam (any rigid construction type) to shape out the block and fit it in before going at it with 'glass. I would, however, advise using polyester or even vinylester over epoxy. Fair using 3M fairing compound or some equivalent and when it's ready do not neglect the barrier coating, like Pettit Protect or Interprotect.

You are correct in pointing out that the IOR legacy of the mid-'70s was in oddly-shaped boats. Olin Stephens commented on this in All This and Sailing Too, saying that too many racing-specific features were incorporated into primarily-cruising boats (he meant, in specific, the winged keel). I can see by your boat's severe deadrise (another IOR rule loophole-beater) that she will heel over till that angle is parallel with the water, which is way too much for a cruising boat. So it shall all come down to how you handle her.

In any event I applaud you for insisting on keeping a boat that, while imperfect, is one you like and believe in. Do the work, enjoy it, and be proud of it. And let us know how you make out with it!

[malbert73]

Originally Posted by dianaofburlingt

I admire you for setting out to remedy this common failing on this vintage of boat. My '74 Hunter 25 has much the same issue, only slightly less egregious. That half-skeg and half-spade rudder combination is the fruit of those times and is at best a performance compromise.

When my dad designed the H25 he included a skeg much like yours, only straighter. When he followed with the Raider 33, a very similarly-shaped boat, he reduced the 'skeg' to a mere dimple. After sailing one, he concluded it should not have had such a skeg at all. It inhibits coming about and light-air performance by holding a low-pressure area alongside it, which is drag. In your case, however, the 'burble' immediately forward to that last vertical edge of the rudder is a worse source of drag. By all means clean it up; and seek the straightest line you can along the bottom of the skeg.

Professionally speaking I do not think your intended improvement is a particularly rough task at all. (I do this sort of thing all the time!) You might even consider using foam (any rigid construction type) to shape out the block and fit it in before going at it with 'glass. I would, however, advise using polyester or even vinylester over epoxy. Fair using 3M fairing compound or some equivalent and when it's ready do not neglect the barrier coating, like Pettit Protect or Interprotect.

You are correct in pointing out that the IOR legacy of the mid-'70s was in oddly-shaped boats. Olin Stephens commented on this in All This and Sailing Too, saying that too many racing-specific features were incorporated into primarily-cruising boats (he meant, in specific, the winged keel). I can see by your boat's severe deadrise (another IOR rule loophole-beater) that she will heel over till that angle is parallel with the water, which is way too much for a cruising boat. So it shall all come down to how you handle her.

In any event I applaud you for insisting on keeping a boat that, while imperfect, is one you like and believe in. Do the work, enjoy it, and be proud of it. And let us know how you make out with it!

Ahh, first we have Bob Perry comment on this forum, and now a Cherubini. What an honor!


I must say that all sailboats should be considered imperfect. While the pinched stern of IOR boats may make for a wild downwind ride, these sterns make for a more balanced upwind ride with less rudder stalling than on today's cohort of cruising wide sterned boats, which reap the rewards of a large cockpit and aft berths. CCA boats like mine boast nice lines, and seakindliness, but suffer in light air with more wetted surface.

Despite all of this, well designed cruising sailboats from all eras (not raceboats) of the same length seem to generally sail at about the same speed +/- 10% depending on which condition they are suited for. Raceboats have made quantum leaps in performance but cannot be cruised comfortably. An imperfect mode of travel compared to advances in cars and planes over the past 50 years, where performance and efficiency probably have improved by 100+%.

Displacement sailing is displacement sailing, and until cruising sailboats can plane easily and safely (canting keels??) the fact that they are all "imperfect" ways to travel is unlikely to change.

[silverp40]

Thanks for the input, I think I will make the change. Not sure if you have seen the previous posts where I posted pictures of the "before and after the fix"?

The very low primatic IS a rule beater as well as a specific design characteristic much like's many of Ted Hood bottoms (see Little Harbor series , Gulfstar 40 and a few others)... efficient in light air, etc.

Insofar as the tenderness aspect, ballast weighs in at 13k - over 60% of total hull displacement keeping these boats from going on the ear too easily.

Cheers
Ovi

[silverp40]

Malbec,

Your Quote:

An imperfect mode of travel compared to advances in cars and planes over the past 50 years, where performance and efficiency probably have improved by 100+%.

Despite all of this, well designed cruising sailboats from all eras (not raceboats) of the same length seem to generally sail at about the same speed +/- 10% depending on which condition they are suited for


Sailboats have been undergoing refinements for probably over 1000 years. Cars, well , about 120 years, but a lot of innovation is happening faster and faster.
Bob Perry said that there has too much true innovation in new in hull design in the last few decades.

What do You think??

[silverp40]

Correction on my post should read:

Bob Perry said that there has NOT BEEN too much true innovation in new in hull design in the last few decades.

(I guess that makes a big difference in the whole idea!)

[minaret]

Originally Posted by silverp40

Correction on my post should read:

Bob Perry said that there has NOT BEEN too much true innovation in new in hull design in the last few decades.

(I guess that makes a big difference in the whole idea!)

I said the same thing here a while back and was roundly mocked for it. Guess it helps to be Bob Perry when voicing such an opinion. The big trend these days is to recycle really old boat design innovations and call them new.