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Extended freeboard spindrift transom mods


pwillems

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Hi All,

First post here!

About to start construction on my Spindrift 11N. I'm planning to build it mostly as designed apart from some minor mods such as an extra 50mm freeboard and probably the seats slightly modified to work so that the nesting bow fits snugly. I'm also planning on using some heavier duty tape on the exterior seams as well as covering the entire bottom section with cloth to improve abrasion resistance.

With the extended freeboard, I am obviously going to need to raise the height of the transom. What I am not sure of is if I should just add the extra 50mm to the transom across the whole width or if I should only raise the sides and leave the middle section at the designed height. I'm mainly worried about raising the outboard by 50mm and how that could possibly introduce cavitation issues?

Any recommendations?

Thanks, can't wait to get stuck in.

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I put a regular shaft outboard on my 11N and it "cavitated" (not really, that is a whole different thing) sucking air. I trimmed the back of the keel and it helped, but I eventually threw my little air cooled Honda 2 hp long shaft and those two are a match made in heaven. I am not sure why you are increasing the freeboard. That boat is pretty darn buoyant. I've had it out in some pretty crazy stuff, and haven't wished for more free-board. She tows great. Put the ring in near the waterline and she tracks sweet when towed. If I was really going to tow it in heavy seas and was worried about tit swamping, I'd make a snap on cover first. 

 

check out these videos. I haven't taken any when its been real rough.

 

https://www.youtube.com/watch?v=9bpO3Xttrtg

 

https://www.youtube.com/watch?v=VO1Azy0Kw7w

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If my math is correct, 50mm amounts to nearly 2 full inches. That seems like a lot to add.  Several years ago someone from the south pacific posted about making spindrifts.........I thought it was more than one for a school or something........but at any rate, he referenced adding freeboard, but only 1 inch.  Don't recall what his reason was but seems to me it was to increase the height of the oar locks or something. It may also be that he felt it needed it for rougher water.

 

Curious what your motivation is for adding that much? In addition to adding a lot of weight, I suspect it might start affecting things like scantlings and perhaps stability?

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Well, while scouring the net for info on the spindrift, I came across a few references to people saying they'd prefer if it had a little more freeboard. I also found somewhere a response from the designer saying basically he saw no problems with increasing the freeboard and to go for if it would better meet the builder's needs.

http://messing-about.com/forums/topic/7905-freeboard-on-the-spindrift/

My boat is going to be used for sail training for the kids at first, but then it is going to become our family car as we circumnavigate. I reckon it's often going to be loaded to the gunwales between passengers and groceries, and will often be used in less than ideal sloppy stuff. So long as it doesn't ruin the boat's other characteristics completely, I am happy to accept the small amount of added windage.

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I wonder what the effects of higher free board would have on ability to recover from a knockdown.  I've purposely swamped my 11N, built really close to spec, and I would describe it's buoyancy as "adequate" at best. I'd be tempted to increase the seat height in bot the bow and stern but I'd check wit the B & B team first.

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I wonder what the effects of higher free board would have on ability to recover from a knockdown.  I've purposely swamped my 11N, built really close to spec, and I would describe it's buoyancy as "adequate" at best. I'd be tempted to increase the seat height in bot the bow and stern but I'd check wit the B & B team first.

 

I would expect that if anything, the extra wood should increase swamped buoyancy. Having said this, your comment is duly noted and I am going to have a think about what could be done to sneak in a little extra buoyancy.

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If you are concerned about abrasion from dragging over shells and other beach shingle, some external sacrificial keel strips may be a better idea than just adding more glass at the seams.  Woven glass is not all that good for abrasion anyway and biax non-woven is much better.  Canoe and kayak shops sell Kevlar tape and/or paste for ruggedizing wear points that works very well.

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I would expect that if anything, the extra wood should increase swamped buoyancy. 

If you mean the extra topside wood it would do nothing to reduce the water captured while righting a swamped boat.  If anything it would capture more water and thus make bailing out harder and increase the foundering during the process.  Raising the seat tops the same amount as you raise the topsides would off-set this, but now you are sitting higher which may have an adverse effect on balance using the boat.  I have rowed my Spindrift 9 with over 600 pounds of weight in it and found it satisfactory.  It was considerably slower, but quite stable and safe.   Not sure I would want that much in a real slop though.  Dunno if that statistic helps any determining if the stock boat will carry a sufficient load for you.

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In a "family car" dinghy I'd rather have a touch too much freeboard than a touch too little.  Speculation about capsize recovery is all well and good but in the uses that you've mentioned for this boat (sail training and family car) you're unlikely to capsize when it really matters - When you're motoring with groceries or grandmas.  When the kids manage to flip the boat under sail it's unlikely to be a survival situation so even if the boat is a little more difficult to right (I'm not convinced it will be) the results won't be catastrophic.

To address your original question - If you're worried about making the transom too tall for the motor maybe you can offset the line of the transom by the 50mm that you'll increase the freeboard and then cut a notch the width of the outboard clamp to keep the motor at the designed height.

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To address your original question - If you're worried about making the transom too tall for the motor maybe you can offset the line of the transom by the 50mm that you'll increase the freeboard and then cut a notch the width of the outboard clamp to keep the motor at the designed height.

Thanks Ken. I note we are almost neighbors. Do you have some pointers to local suppliers for marine ply, epoxy and glass? I was about to order online, but would prefer to get it locally.

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   Try AJW Shipwrights for plywood.  I think he might carry Bote Cote epoxy, too.  I live in Yangebup and he's just across the railroad tracks from me (Bibra Lake?)  Tell him I sent you.

   If Aaron at AJW doesn't carry the goo he might refer you to Gary Martin at Fremantle Boat Paints.

   If plywood transport is difficult I may even be able to help since I have a ute and relatives in Karnup so I end up in your neighborhood once in a while.

 

   Also, have you heard of the Old Gaffers or the Amateur Boat Builder's Association (ABBA) of WA?  (They're not suppliers, just local boat enthusiasts).

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   Try AJW Shipwrights for plywood.  I think he might carry Bote Cote epoxy, too.  I live in Yangebup and he's just across the railroad tracks from me (Bibra Lake?)  Tell him I sent you.

   If Aaron at AJW doesn't carry the goo he might refer you to Gary Martin at Fremantle Boat Paints.

   If plywood transport is difficult I may even be able to help since I have a ute and relatives in Karnup so I end up in your neighborhood once in a while.

 

   Also, have you heard of the Old Gaffers or the Amateur Boat Builder's Association (ABBA) of WA?  (They're not suppliers, just local boat enthusiasts).

Thanks Ken. I really appreciate the offer but I also drive a ute and should be OK to transport the ply. I'll pay Aaron a visit soon.

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  • 1 month later...

It isn't just flotation, it is comfortable seating for sailing.  As the builder and owner of a Spindrift 9 nesting I would never recommend the nesting version unless there was a really big need for taking the boat apart.  Some people have that need, but I don't think most of us really do. (myself included)

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