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Old 11-20-2001
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Modify aluminum hull/keel

Has anyone ideas on the feasability of modifying the fin keel on an aluminum IOR racer to suit cruising needs? The objective would be to take an 8'' fin, shorten by 2'', add a lead bulb to achieve a safe righting arm and extendthe keel fore and aft to cover the full length of the bulb to minimise chances of fouling. I realise it would require the services of a naval architect, but is the basic idea impractical?
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Old 11-20-2001
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Modify aluminum hull/keel

I would imagine that it can be done but it won''t be easy or cheap, and I am not sure that you will like the results. Structurally, I am assuming that you have a typical IOR era bolt on lead fin with or without an aluminum sump. (I am figuring lead since iron would have horrific galvanic action problems)

During the IOR era these keels were generally cast with integral keel bolts with a hooked end on them. In other owrds, these bolts would extend almost to the bottom of the lead and would have a hook rather than a nut that held the bolt in place. If you simply cut off the end of your existing keel you will risk cutting through the bolts and so will not have a good connection any longer. So to begin with you are probably talking aboat a new keel casting as well as casting a bulb.

The nice thing about an aluminum boat is that you can cut and weld almost at will, which is expecially important in this case.

You will probably have to rework the internal structure. Most aluminum IOR era boats had a system of fore and aft longitudinal stringers and athrwart ship frames. In the bilge at the area of the keel the athwartship frames (called ''floor timbers'' or simply ''floors'')were generally larger than the frames fore and aft of the keel and mast step. There was also typcially a keel stringer on either side of the bilge that distributed the loads fore and aft. To lengthen the cord of the keel you would need to add additional floors and lengthen the keel stringers. Some IOR era aluminum boats also had a space frame and that may need to get completely reworked as well. Its a lot of work but it is do-able.

The biggest concern is the sailing ability of the finished product. IOR boats generally were tender,comparatively heavy and undercanvassed compared to non rule boats of the same era such as the J-35''s or Farr 11.6''s. They used a hull form that was very dependent on crew weight on the rail. It was less than ideal for general purposes. So here''s the problem, you need to maintain at least the original stability, and ideally get more stability than the boat originally had. If you are going to do that in a shallower keel you are going to add some combination of more weight and more surface area. These were already under canvassed boats so you will be giving up speed to the drag of the greater wetted surface and the greater imersion and the increased weight. So then you need to look at the rig a bit. and if you look at the rig you may need to look at the structure supporting the rig. And so goes a viscious circle.

So like I said, Its not easy or cheap and you probably won''t like the finished product.

BTW How big a boat is this anyway?

Regards
Jeff

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Modify aluminum hull/keel

Thanks for the thoughtful reply, Jeff. I don''t (yet) have such a boat, but have been window shopping for the past few months, expecting to begin real shopping early next year. The market usually has several 50+ foot aluminum Frers or S&S designs from the early 70''s. If I''m going to buy an older boat in need of updating, my thought was to start with one of these rather than a GRP boat.
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Old 11-21-2001
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Modify aluminum hull/keel

If you are talking about the early 1970''s (before about 1974) you are looking at IOR I boats. These were not too bad, but are a real handful to sail shorthanded or down wind. Compared to the IOR II boats that follow, IOR I are comparatively robust,stabile and slow.

The FRP in use before 1972 tended to be less prone to blistering and also more simply engineered than the boats that follow shortly thereafter. Aluminum technology of that era was extremely primitive when compared to modern alloys, welding and forming techniques, engineering, and electrolysis protection. Making things worse is that the big aluminum racing machines of that era were not designed to be long lived. They were designed to push the envelope and win races.

There are a number of things that I would be concerned with in an aluminum IOR I boat. I would be concerned about fatigue at frames, in areas where the hull plating had a lot of shaping, and near the keel to hull joint, and deck to hull joint. Many of these aluminum boats of this era had glassed over plywood decks which are prone rot. Forming and welding techniques resulted in terribly unfair hulls that would be faired using massive quantities of filler. While epoxy and microballons were coming into use, these fillers were often polyester based. At some point the adhesion between the fillers and the aluminum will give up and you can be facing a problem that makes blisters seem like a walk in the park. I saw ''Tenacious''being refaired after the Fastnet Disaster. I could not beleive how bad her hull looked before the refairing and how much material went into refairing her.

Jeff
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