Eun Mara - wood instead of steel bilge boards?

[almeyer]

I'm studying plans for Iain Oughtred's Eun Mara. The design shows twin bilge boards and a lead ballast keel. The bilge boards are fabricated of 3/4" steel, then galvanized, and weigh about 90 lbs each. The ballast keel weighs approximately 400 lbs.
I'm considering making the bilge boards of wood, with lead inserts to keep them from floating, and making up the difference in weight by increasing the width of the ballast keel. As I see it, this approach has several advantages:
- I can make wooden boards, but would have to pay a shop to fabricate the steel boards. I don't have any equipment or skill in metalwork. I ran some numbers, and the lead weight required to keep the boards from floating is small enough that I can pour the weights myself.
- The ballast keel is large and heavy enough that it will have to be shop-fabricated. Whether the keel weighs 400 lbs or 500 lbs is irrelevant; I can't pour either one myself.
- The plans show a winch assembly to raise each steel bilge board - more shop-fab'd items. If my number crunching is right, I wouldn't need a winch with the wood boards; a simple lanyard would do the job.

I intend to submit my calculations to the designer for his review before I proceed, but before I do, I'd like the Forum's thoughts: Does this seem like a feasible approach, or am I missing something and this is a goofy idea to begin with?

Thanks, Al

[StevenBauer]

I think it's worth looking in to. Time to write Iain a letter. :)


Steven

[Woxbox]

I'd want to do it that way myself. Did you catch the related thread on trying to shape a steel board? I'm interested to hear what Ian says.

By the way -- be generous in the amount of lead you'd put in a wood board if you want it to go down reliably. They can hang up very easily. But yes, you'd still be able to raise it by hand.

[StevenBauer]

I seem to remember some discrepency with Howard's steel boards. He made them a little thinner than called for but they weighed more than specified?

Steven

[kenjamin]

My experience is that Iain Oughtred is very prompt about responding to snail mail but he also answers the phone if you're in a hurry. (Sorry, you'll have to search for the number.) He gave me permission to try out my storable birdwing mast on a Caledonia Yawl. Doing away with the winches seems like a good idea to me. You could probably get a more efficient foil shape with wood as well.

[Dale H]

Do check with Iain first but I can almost guarantee it will be OK. I know of a centerboard version being done this way, with Iain's approval.

Good luck with the boat!

Dale

[Thorne]

There are a lot of websites covering various builds of this boat, but most seem to have followed his instructions as to metal bilge-boards.

http://www.geoss.com.au/eun_mara/ian_dunedin2.htm

I'd worry about sideways strength of BB's made from wood -- if the boat hit bottom and dragged sideways, sure seems like you could snap a wooden BB. Also, is there ever a case where the BB is used as a prop or stand -- like beaching the boat or a in a harbour with a large tidal change? Again the metal might be better than wood for that usage.

[Woxbox]

if the boat hit bottom and dragged sideways, sure seems like you could snap a wooden BB.


Thorne -- I wold say this is a good thing. Much better than breaking the centerboard case free of the hull!

[Thorne]

If that is the only option, yes. But if the CB is steel and the CB case properly reenforced, it shouldn't happen.

Just wondering if the designer is relying on all the foils being metal for other reasons than providing a CLR. If you wanted to take the ground, you'd have the CB fully up, but might want to have one or both of the BB partially down to hold the boat upright as the tide goes in or out.

[StevenBauer]

Al, if you were going to use electric power like on Paul Fredrikson's EM the batteries could make up for the weight loss and you could stick with the original size keel. Just a thought.

Steven