Forward Raked Daggerboards ?

[mcm]

Chris White, in "Cruising Multihulls", suggests that a forward raked daggerboard should slide back up into its case without causing damage when grounding or striking a hard submerged object.

Does anyone have any experience or opinions about Chris White's suggestion ?

 

[catsketcher]

My daggerboards in my 38ft cat rake forward 3 degrees - does bugger all. In my small trailer sailer cats my boards go straight up and down but the cases are rectangles rather than daggerboard shaped. I don't use a hold down but rather let the board settle. When I hit the mud the board does go up but it stays on the bottom. I haven't worked out a way to get it to retract. I think case design and build is really important - big flat back to the case with corresponding flat back to board.

Problem is this design bangs around whereas the big cat's cases are silent which is very nice offshore.

Choose your poison

Phil

 

[mcm]

32deg. forward rake is illustrated on Chris White's example of self retracting daggerboards.

Phil, that may explain why your 3deg. forward rake doesn't do much.

 

[Corley]

Personally I don't buy it as even at 32 degrees of rake it would surely still only be a possibility it would slide up the case. It would also depend what you hit if you hit a rock ledge angled or not it would be a solid board breaking impact in sand it's just as likely to dig in if it's a firm mud bottom maybe it might work as long as it shelved gently. It could be argued that an elliptical type daggerboard tip in a vertical case might be as effective in a shelving situation or at least reduce the loading.

I've read a few articles dedicated to this concept and I'm not satisfied that any of them have made an adequate case for a certitude of daggerboard retraction on impact. They mostly use a lot of comments like should or might or possibly so in essence where are the real advantages? You still have to build a very strong daggerboard case just in case the retraction doesn't work as planned. A forward raked daggerboard must also be effective for catching kelp and other debris that might be floating near the surface.

By the way I'm certainly not against the idea but on balance there doesn't seem to be any evidence it would work. If a few boats were built this way and have proved themselves in the field I'd certainly be interested to know.

 

[Gary Baigent]

On my old Bamboo Bomber catamaran Supplejack, we had a couple of degrees raked forward daggers and when I stupidly sailed in too close to East Coast bays trying to sneak the last few metres, we hit reef ... and the boards did pop up - which definitely saved us/my embarrassment. These were foil shaped cases. Didn't leak either. Maybe I/we just got lucky.

 

[snowbirder]

Also, I think there is a good argument for planned breakage, where the board is weaker than the trunk.

 

[catsketcher]

I have the planned breakage boards on my 38ft cat. When I made the boards I got close to finishing then cut off the bottom 300mm and then glued it back on again. Better than breaking the board I guess. I even made extra board bits in case I break the ends off and can't pick them up. After 15 years I haven't broken them off or hurt a board.

cheers

Phil

 

[jamez]

If surviving kick up on grounding is the issue just use a trad front hinged centreboard. I tend to rely on a chart to point out shallow water myself.......

 

[snowbirder]

If surviving kick up on grounding is the issue just use a trad front hinged centreboard. I tend to rely on a chart to point out shallow water myself.......

Seriously. In over 20 years of very regular, year round sailing, I've touched the ground once. Inside the ICW where the channel silted up. Big lump of soft stuff mid channel.

 

[catsketcher]

No centreboard

Jamez

There are too many problems with a centreboard that I wouldn't have one again in a boat I owned. It must be the way I sail but I run aground often - I push up creeks, over sand bars and the like. I run aground far more often than a typical sailor because my boat lets me off when I do. It is one of the essential pleasures of multi owning.

My depth sounder stops working about 50cm before my rudders hit. The boards are usually well up at this stage. If we touch then I jump off and push - waist deep. You can't be blase unless you know the bottom is benign but I have stopped in some gorgeous places - 10 days in North Zoe creek for example - because I am fine with touching bottom if necessary.

cheers

Phil

 

[normancook]

Hello everyone: for those of you who are building a cat and are looking for the Holy Grail ...that is a Daggerboards that retreat into a foil slot equivalent to the board shape ...what you are looking for is a SCABBOARD which can be canted forward and will retract regardless of the type of impact. The Scabboard can be removed from above deck but does not extend from extend above same when retreated & stored.