sealing washer for a keel bolt

I have been set an assignment requesting various types of suitable material to make a keel bolt washer. It makes ref to a rubber hose type material DTD625 I must select the most suitable by comparing the differences and then making a final selection. I have researched this subject now for the last 2 days and have gotten no where. Could someone please list a grade of washer say 316 stainless steel / neoprene /fibre or at least explain why it is so difficult in responding to such a simple question. Is it because there is no answer

 

I don't know what type of material you are putting this bolt into, but it must be hard (metal) or you wouldn't be having a problem.

I think that the reason you have not had a reply to this question may be that any soft material that can seal the bolt will not survive the pressure placed on the bolt when you tighten it. It will simply "squish out" if I understand your question correctly. It may not be appropriate for your application, but you might want to consider cutting a small groove in the underside of each bolt head to accept an O-ring. A very thin O-ring would work well (there is very little pressure involved), and all the pressure on the bolt would NOT be transmitted to the O-ring material, but would be limitted by the groove dimensions. You can get groove design data on the web from many of the O-ring suppliers. (For example: http://www.marcorubber.com/gd-directory.htm)

This would be a pain, to be sure, but the O-ring is an extremely effective sealing device that should last indefinitely.

 

Neoprene comes in a variety of hardnesses, you would need one of the harder varieties.
Depending on the material of the keel bolts, I would use the same material for the metal washer and nuts (Bronze with Bronze) etc , with the neoprene between the wood and washer.
Thick or doubble washers with a large surface area is best.

Tough neoprene won't squish out ,the wood keel will be crushed by the bolt tightning , if you go that tight.

FAST FRED

 

The quick answer is that the washer does not seal the hull/keel joint. That is accomplished at the mating face irself. The washer is purely there for the nut to land on, and in some cases to help spread the load.
Steve