16' Keel boat-high performance

Do you think a canting keel is worth the extra trouble on such a small boat? Backman 21 has one with 225kg bulb, while B18 has only 100kg ballast so it isn't much to move around compared with the crew.

 

Sdb

Raggi, I was all for it until thinking of the sliding deck ballast system which seems far superior on a small(16-18') "sit in" boat.
See the last few posts; it would be interesting to hear what you think of the idea.....

 

OK, I didn't read page 2
Well, I think the boat will be faster with just the crew.
A bulb on a dingy is more for extra safety or peace of mind than for speed.
How safe will the boat be with on deck moveable ballast?
Maybe a trimaran is better?

 

A boat with wide wings and a trapeze might be faster on some points of sail, but would demand an athletic crew and considerable practice. The sliding wing would permit placing a fair amount of ballast a long distance from the hull, and thus permit a one person sit-in boat to be competitive with most two place trapeze boats.

 

Wouldn't it be great if there was a Backman 21 for the self-builder, full NC files for frames and aluminium skinned.?
Just have the frames water cut, a jig, and home welder, Bingo!.

 

Well, we have the Backman 18

 

18 & 12 SDB(Sliding Deck Ballast) boats

RC, you've got it exactly right.
An 18' SDB : 220lb sliding ballast in 10' Trapwing™; Max crew 250lb.; retractable daggerboard with 75 pounds ballast, cants 20° each side with simple V trunk tied in to SDB system. SCP/total weight= 30%
180lb.hull;plus rig and foils. 785lb. all up displ. with 250lb. crew;255sq.ft. SA(upwind); S/D=48 -- better than most dinghies and nearly the same as an I14.----Capable of upwind planing and even faster w/o ballasted daggerboard and with a lighter crew.Extremely large crew weight range at max performance from 120 to 250lb. Capable of foiling....
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12.75' SDB, 130 sq.ft. SA, 8'Trapwing™ with 76 pounds sliding ballast; 426lb max displ. with 250lb crew. 130sq.ft. SA; SA/D= 36.82(comparable to 505&FD.) SCP/total weight =30% with max crew.
Extremely wide range of crew weight at maximum performance -90lb. to 250lb.(90lb. crew requires 20lb. more ballast in Trapwing™); 200lb. or less crew capable of foiling.....
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Trapwings would have molded buoyancy pods on the ends; whole wing slides; 18' system could be electric w/o much additional weight; est. 30 pounds incl. battery. Weight plus crew also slides fore and aft on both boats; boats would have AT LEAST rudder t-foil.
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The more I look at this the more I like it......
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From Mr. Bethwaite: SCP = sail carrying power; it is equal to the max Righting Moment divided by the Heeling Arm. SCP divided by Total weight gives a percentage-according to Mr. Bethwaite if 30% or over the boat will plane to windward. It is the only comparative ratio I know of that includes the boats RM & power to carry sail.

 

Hey Raggi,
Excellent idea, now do it in Aluminium, I don't do wood.

 

L Francis Herreshoff In "The common sense of yacht design" mentions a sliding ballast system on a yacht of his Grandfathers in 1860
And another by his uncle in 1862.
See page 119..page 120 shows a canting keel
This idea is not new at all,just has not been used because of dam racing rules which have stifled the development of yachts since racing started.

 

OK, if you help me with the scantlings, we can do that.
We already use a laser to cut the plywood, so cutting aluminium is no problem.
We used 6mm Okume for the frames, we are no changing to 8 or 9mm because it's easier to fasten strip planking then.

Send me an email if you are serious

 

Raggi,
I am working on my own project at the moment.
It will look like a Dragon above LWL with a detachable bulb keel below.
I will show it here for the NA's flaming once I have it to a workable stage.

 

SDB(Sliding Deck Ballast) boat(s)/Trapwing

Tactic, I read that one of the Herreshoff's considered his SDB boat his favourite..I've used variations of the system since 1995 on various model boats and have incorporated the best features into the 18 and 12.75' versions. The weight slides side to side and the whole Trapwing™ moves. The wing and crew can move fore and aft simultaneously. The Trapwing™ is supported by one "trapeze" on each side and the whole wing pivots adjustably in relation to the hull.The Trapwing uses buoyancy pods molded into each end that have buoyancy in excess of the ballast carried in the wing.
My version of sliding ballast allows tremendous power to carry sail (SCP/displ=30% or better- WITH a 250lb crew!) while allowing an extremely wide range of crew weight(90-250 lbs.). The system lends itself to a weight equalization scheme that will keep all boats the same weight with equal righting moment. It allows movable ballast to do much more, in terms of righting moment, than any form of canting keel.
It should give a disabled or able bodied sailor a "sitdown inside" sailing experience unmatched by any boat curently being built that I am aware of. I have been pleasantly surprised at just what a boat using this system is capable of and that it can be effective on as small a boat as 12.75' LOA(having the same wide range of crew weight as the 18 @ max performance).
The wing pivots in the side to side plane relative to the hull alowing up to a 20° angle of heel with the wing level AND also pivots when viewed from above so that for trailering the wing is simply rotated in line with the hull keeping the maximum trailerable beam to 4' or under for both the 18' and 12.75' versions.
Both boats are designed to be beach sailable with or without hydrofoils.
I think it's an exciting concept and I'll just have to figure out how I can build one.....

 

Doug,
I am glad you finally came to realize that the canting keel would not be optimum on boats of this type.
You will remember me mentioning a sliding ballast system in our disscussions several years ago.
I had another idea today...water ballast system with the water in Pods..the leeward pod also acts as a stabilizer when the boat is heeled greatly(Ie prevent a knockdown).
The water is simply dumped with gravity before each tack,and no water needs to be carried on light days.
Havn't worked out any details at all..just an offhand thought that I had today,may not work at all.

 

I have thought about such a system extensively, my one concern is that it would be difficult to pump the water in rapidly enough. This could cause problems on a rapid tack, as the sail would have to remain depowered waiting for the ballast to come in. Much of the advantage would also be offset if you permitted adjusting the amount of ballast in the wing.

 

What about water in a moveable tank. That's faster than pumping, and you can move it after or at the end of tacking.