16' strongback for a 16' Prospector...?

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tszpieg
Posts: 44
Joined: Mon Apr 09, 2007 9:51 am
Location: Ada, MI

16' strongback for a 16' Prospector...?

Post by tszpieg »

Good morning Everyone,
I've been doing some searching and have found mixed reviews about building a 16 Prospector on a 16' strongback. I just completed my (of course) 16' strongback that I intended to build my 16' Prospector on, which leads me to my questions...
Should I cut off the ends of the strongback, and if so, how much should I cut off?
or
Should I add some distance to the overall height of my forms when I cut them out to raise the stems to a workable height above the strongback? If I go this way, how much should I add to the forms?

Are there advantages/disadvantages to going one way or another?

I also have a question about my strongback itself. It has a little lateral (side to side) wave in it from end to end (I have not attached the top plate yet), and when I checked the top edge for being straight from end to end (using string) there is some variance there as well.
From what I understand, and please correct me if I'm wrong, the lateral wave may straighten out when I attach the top plate. As long as my top, and center line are straight I should be okay there, right? However, before I attach the top plate, should I shim out the dips with playing cards so that is perfectly straight with a string line?
I think my plywood warped a bit between getting it ripped and putting the strongback together....
Any help/ideas would be much appreciated.

Thanks, and have a good one.

Terry
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ealger
Posts: 387
Joined: Sat Aug 14, 2004 5:14 pm

Prospector Strongback

Post by ealger »

Terry, not to be sarcastic in any way, my dentist once told me to only floss the teeth I wished to keep! I guess what I mean is just how much effort do you wish to place on getting the foundation set for your build which you'll be looking at for possibly the next year.

This is a photo of how I mounted the Prospector stem over the strongback:
Image

The overhang is 12". You can see the mark of the shearline which is only 1" above the bottom of the stem mold.

There have been lots of Prospectors built on 16' strongbacks and using molds cut to the plan dimensions and there are pictures on this site showing so. However, it's been suggested that if the strongback must be 16', then add 2" to the bottom of the forms. The clearance at the stem ends is necessary to allow working room for adding the glass.

Side to side wave, while annoying to me, can be overcome by laying out a straight center line on the top deck. Any dips along the length or width of the deck should be corrected elsewise you'll be compensating later when you attach the molds. I use a laser level to level and flatten out the top deck before applying the molds. I find this makes life easier when leveling out the waterline marks on the molds.

The other question is are you building the strongback per CanoeCraft?


Ed...
http://s12.photobucket.com/albums/a237/ ... 6/?start=0
Ed Alger
tszpieg
Posts: 44
Joined: Mon Apr 09, 2007 9:51 am
Location: Ada, MI

Post by tszpieg »

Thanks for the info Ed. I do appreciate it.
Yes, I have built the strongback per the instructions in CanoeCraft. It was pretty straight forward, other than my plywood warping like it has.
I'm thinking that I will cut 6-8" off each end of my strongback. I figure it will make this build that much easier, and I can always extend it if I need to for a longer boat in the future...

A question about your forms... Looks like you're using MDF, correct? I had intended on using 1/2" plywood, but I do not want to risk my forms warping at all. Maybe I need a higher grade plywood..? Would you suggest using MDF rather than plywood? I've noticed other people using MDF. Is that more stable with the humidity? I live in Michigan and it does get pretty humid around here in the summer.
I do intend to build stapleless, if that makes any difference.

You boats are beautiful, by the way.

Thanks again for the help on this one.
I'm learning more and more as I search the archives of this site.
What a great resource!

Have a good one,

Terry
canoeblderinmt
Posts: 415
Joined: Sat Jul 03, 2004 12:04 pm
Location: Butte, MT

Post by canoeblderinmt »

Terry,
My thoughts on warping are that width equals straightness. I always use 3/4" ply for my molds for this reason. More plys, so more stability. I don't trust 1/2" stock to stay warp free. I know that many builders use it with fine results. For me, it's not worth a few bucks to take the risk. I know I will probably build more than one of each boat I build, so I want my forms to last.

I will be watching your build with interest, as the 16' Prospector is my next build, if I ever get back into the shop. I am engaged to a woman with twin 5 yr old girls. We have recently taken on 3 grandkids, 6, 3 and 11 mos. It may be awhile before I am covered in cedar sawdust again.... :sad

Greg
" Choose to chance the rapids, Dare to dance the tide..."
Rich from Rockford
Posts: 12
Joined: Thu Feb 16, 2006 8:04 pm
Location: Rockford, MI

Post by Rich from Rockford »

Here's a picture of a Prospector using the full 16' strongback. I raised the moulds 2" for some clearance.

Image

So far it hasn't been too hard working this way, although I think the extra access would be worth cutting it down - it probably wouldn't be too tough to add it back on if you're going to use it again for a longer canoe.. I don't have the storage space, so my strongback, if it can't be used for a bench or something, will probably be taken apart.

For the moulds, I unfortunately used what I had lying around, including OSB, 3/4" veneer ply, and some 1/2" ply. The main reason I went stapleless was finding out the OSB would't hold the staples well enough.
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ealger
Posts: 387
Joined: Sat Aug 14, 2004 5:14 pm

16' Strongback

Post by ealger »

Terry, I've used 1/2" MDF since I started building Cedar strippers. It stays absolutely flat and it takes a pencil line beautifully when tracing out the templates. I build stapleless and cut a 1/4" x 1/4" clamp groove about 3/4" from the edge. I use a router to cut the groove.
The other reason I like MDF because it sands easily. I set my molds so that strip will contact the full surface of the mold. This requires sanding the mold edges. This method also requires that the mold be aligned on the strongback to the opposite edge than is shown in Canoe Craft.
Ed...
Ed Alger
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Adamv
Posts: 109
Joined: Fri Mar 04, 2005 1:40 pm
Location: Owen Sound, ON Canada

Post by Adamv »

Terry, I just finished my first build (15' Bob's Special) and used 5/8" MDF for the strongback and 1/2" MDF for the molds. The MDF worked very very well for both. Takes a pencil line well, is very stable, and cuts and sands well. The only drawbacks I experienced were the heavy weight and the extra need to wear dust protection when cutting it (if I understand correctly, it has a good amount of chemicals in it that are pretty nasty on the lungs). The weight actually was a bit of an advantage for the strongback, as it helped to keep it firm on the ground (I did not fix it to the floor). I will certainly be using MDF for my next build.
Who travels not by water knows not the fear of God --- 17th Century Sailor
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