Scud or Warwick 24 - Wooden boat with stainless steel and aluminum lift keel !

[boony]

Hi all

This thread is following on from two previous threads, but I have decided to create a brand new one where all advice and info can be kept together, and the curious can follow and commiserate. Many thanks to Boatdesign.net for creating this forum.

Ok for those just jumping in, I have a peculiar setup where I have a lift keel made of stainless steel with an aluminium case. Most people say that this is definitely a bad choice of materials, but there is very little corrosion and they have been sitting side by side for at least 10 years.

The boat is a Scud, also called a Warwick 24, designed by Alan Warwick of NZ, and built of double diagonal moulded ply. There is a single chine starting a quarter of the way back from the bow and running all the way aft, just above the waterline. Deck is ply. The boat was supposedly designed with a daggerboard. It is 20 years old.

Ok the next bit is what the previous owner told me. Originally built professionally in NZ by S. Connors, it somehow arrived in Oz, where it so happened the original shipwright was now living. He bought it and modified the lift keel setup. During its hectic life it has been Parramatta River SC champion from 1991 to 1996. (I have yet to check this out).

The daggerboard was replaced by a stainless steel foil with a lead bulb. The foil is guided by an aluminium case which runs from the hull to the deck. The keel is lifted by a hydraulic ram and pump via a pulley in the deck. The ram and pump are bolted to a steel strut. The strut is bolted through a bulkhead to the keel case, as well as being screwed to the boat frames. Who ever did this thought stronger never hurt anyone, but I really think there is too much weight in this whole set up. The hydraulic ram, pump and steel strut weigh some 30/40 kgs together ! Then comes the aluminium case which weighs about 20/30kg ! (Oh and about 2 kgs worth of nuts and bolts).

Ok now for the keel. The foil weighs approx. 50kg and the lead bulb supposedly 400kg. The foil has a stainless steel skeleton for strength, with wood used to create the profile. The whole lot is covered with several layers of fibreglass. I have since stripped this to renew.

I am refitting and repainting the boat. I have never sailed it having bought it from its previous owner while it was on hardstand. While there was a risk in purchasing this way, and it does need some TLC before any problems become chronic it had a positive survey. This is also the second boat I am renovating so I know what I have let myself in for ………….oh why, oh why, oh why !!!

Ok here the questions from my previous thread along with some pix.

1) The boat is now on hardstand and i have pulled everything out for the refit. Because the edges of the aluminium case have become very uneven due to the corrosion and some water was starting to weep through the hull and case join I was thinking of replacing it by a stainless steel case. I am yet to get quotes, and am on a somewhat tight budget.

Questions

- Should I make every attempt to have a stainless steel case built, or is it acceptable to repair the aluminium case given its past resistance to corrosion ?

- If I keep the aluminium case what are the ways i can isolate it from the stainless steel to avoid future corrosion ?

- last question and quite different ; according to the shipwright the keel has a poor profile, and I would gain by improving it. The keel is basically a straight blade with a lead bulb on the bottom. I've heard of NACA profiles, but I really don't know where to start my research, and any info needs to be accessible for an amateur like me. Thus far what i have found is way above my head. Apparently there is a formula available too for this sort of thing. Can anyone point me in the right direction ?

[hansp77]

Hey Boony,
How goes things?
Any decisions on your keel case?

Have you found out prices yet to repair aluminium or to build new stainless?
I would think that to repair aluminium would probably mean to build anew, thus making it tempting to just go with stainless.
(Beware of my reasoning, if option A costs is close to effort and price of option B, and option B being more expensive is better, then option B should be taken…)

I am no designer, far from it, but, the profile of your keel seems to match rather closely some of the dedicated racing boats down at the yards that I have seen.
I mean it keeps the wheight down as low as possible, where you want it, and in between offers as little forward resistance as possible and a lot of sidways resistance, also what you want.
But please, designers, step in if I am wrong.

also, have you started stripping paint yet?
Any luck with that heat gun?

P.S Nice boat.

Hans.

[MikeJohns]

You would be better off with a GRP case , you could build that yourself and it would affix well to the ply hull.
The dissimilar materiasl are just an automatic self destruct.

Keel foil shape is often better if the foil shape is less of a flat plate and more of a NACA type foil making the foil wider in section also reduces the stresses on the foil.

IS this boat removed from the water when not sailing?

[boony]

Hi ya MikeJohns,

Thx for the reply. Not sure if a GRP case would be structurally strong enough. I have been thinking of a building a stainelss steel frame for structural strength, and using ply panelling on the sides to save weight.

Once completed this boat will be sitting in the water most of the year, so there is an issue with corrosion of metals or rotting of any wood of the submerged part of the case. Given the difficult access, I will be unable to check this on a yearly basis.

Cheers