mast step strength super dooper sunfish hull speed

nikobrogna

nikobrogna

New Member
hey guys,
I am in the middle of fixing up an old sunfish. I plan on rigging it with my own "super dooper sunfish rig." I have designed an 80sq. foot, fully battened baracuda rig, with a stayed 20' mast. The boom is 7 1/2'. I have made scale models and drawings, and have made sure that the center of effort of the new sail remains in the same spot as the normal rig, which is just about right over the daggerboard (I am also making a foam and plywood cored, larger daggerboard). Therefor, the boat should have the same windward/leeward balance as the original rig. I plan to set up a forestay, and two aft, lower shrouds. To avoid putting stresses on the deck that would be pulling it off the hull, the shroud and stay fastenings will be throughbolted into the lip that runs around the hull- does this make sense? All other cleats and hardware will be attached to the rig itself- the halyard cleat, vang hardware, etc.

My question is, How strong is the mast step of a sunfish? For that matter, the mast step of a PEARSON made sunfish. Will it be able to withstand the downward pressure of the afformentioned stayed rig? Will I have to reinforce it? I will be placing a deckplate in that area anyway, to do other repairs.

Also, I know that the top hull speeds of displacement boats are limited by wave action. Are there any barriers that limit the top speed of a planing hull, like say, a sunfish?

thanks,
-Nick
 
Fairly new to the Sunfish but have decades of experience with a zillion other boats.

The headstay and shrouds are introducing all sorts of loads that the hull was not designed to accommodate. Mast step loads although considerable will be the least of your problem. Fore/aft loads between the mast and bow and compressive athwartship loads at the shrouds might be the greater demons.

All might work if you remove the deck and install a proper load bearing structure. The hull itself won't do it.
 
Nick,

Interesting proejct. Redboat's reply above is correct. To attach stays to a mast, one needs chainplates at the bow and both topsides a few inches aft of the mast hole, and the hull was never made to take this kind of load; the topsides especially are too thin. You could install three inpection ports, one on each side adjacent where you are placing your side chain plates and one near the bow. Then epoxy in a fairly long piece of, say, 1/2" marine plywood inside the topsides port and starboard and then bolt a stainless steel tang externally and attach your side stays to these tangs. The long board on the inside of the hull will spread the load out and might just work (or the topsides could pull out with the first good gust you encounter, the reason why God invented PFDs.) As for the bow, stand the hull on its nose and lay up 8 or 10 layers of epoxy resin and fiberblass mat or cloth the then bolt the bow tang though the bow externally and attach your bow stay to it. The mast hole and the side stays will take most of the load so the bow stay is not as important as the side stays. I owned a little dinghy once that had a fairly massive mast hole, no side stays a very small diameter bow stay that was there to keep the mast in place in the event if a capzise and to help control the mast bend, and this rig worked fine.

If you have an old hull that you don't mind destroying if your back-of-the-envelope calculations turn out to be wrong, this might make for an interesting nautical experiment.

Alan Glos
Cazenovia, NY
 
Nick,

Interesting proejct. Redboat's reply above is correct. To attach stays to a mast, one needs chainplates at the bow and both topsides a few inches aft of the mast hole, and the hull was never made to take this kind of load; the topsides especially are too thin. You could install three inpection ports, one on each side adjacent where you are placing your side chain plates and one near the bow. Then epoxy in a fairly long piece of, say, 1/2" marine plywood inside the topsides port and starboard and then bolt a stainless steel tang externally and attach your side stays to these tangs. The long board on the inside of the hull will spread the load out and might just work (or the topsides could pull out with the first good gust you encounter, the reason why Got invented PFDs.) As for the bow, stand the hull on its nose and lay up 8 or 10 layers of epoxy resin and fiberblass mat or cloth the then bolt the bow tang though the bow externally and attach your bow stay to it. The mast hole and the side stays will take most of the load so the bow stay is not as important as the side stays. I owned a little dinghy once that had a fairly massive mast hole, no side stays a very small diameter bow stay that was there to keep the mast in place in the event if a capzise and to help control the mast bend, and this rig worked fine.

If you have an old hull that you don't mind destroying if your back-of-the-envelope calculations turn out to be wrong, this might make for an interesting nautical experiment.

Alan Glos
Cazenovia, NY
 
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