Prospector stem mold to station 6

[lamarkeiko]

Hi all readers of the builders forum. I'm a new canoe builder, and have a question that I hope to get answered before I go any further on building. First let me say that I have a Canoecraft book that I've read through, and I have a copy of Bear Mountain Prospector plans which I am using for my forms. I have completed the strongback, the stem molds, steamed and glued my stems and made station 6 molds. My problem is that the top of my inside stem does not line up exactly with the top of station 6 mold when butted together. My inside stem is about 1/4" higher than station 6. I've double & tripple checked my molds to the full size plans, and cannout see where I went wrong The plans of stem mold measure exactly 22 1/2" high from base line where it butts against station 6. Station 6 plans measure just slightly over 23" from baseline to top of mold. When 3/4" thickness of inside stem is added, I'm 1/4" high. Did I misinterpet somthing on the plan drawings, or is this normal? If this is normal, do I plane down inside stem mold to be flush with the top of station 6? Any advice is appreciated.

Lamar

[frugal]

I was hoping that someone else that has used plans would respond but it looks like that might not happen.

I didn't use plans for the Redbird we are making but used the offsets from Canoecraft. I checked the book for the Prospector and station 6 height is 23" plus 1/16" so what you are seeing there looks right.

I am assuming that since you purchased plans, these would be accurate. I can't find a reason for you to be out by 3/16".

At this point I would probably just shape the inner stem using the forms as they are right now. A lot of people don't use inner stems so you shouldn't need to worry about the slight compromise there. However, take any advise from me with a grain of salt. I'm just saying what I would do.

[canoeblderinmt]

I build stemless (wonder why?) so I may be off base, but just looking at it from a joinery standpoint, I'd consider shaving the 1/4" off of the "inside" if the inside stem; i.e. the part against the form. The "outer" or "upper" part is already formed to meet the outer stem, changing the geometry might cause you problems later.

Greg

[frugal]

Your comment regarding joinery is something to consider. However, the stems were formed by steam bending them to these forms. If you take 1/4" off the indise, they will not match the forms anymore.

As for the joinery problems that might be encountered later with the outer stems, you might have explained why my outer stems did not match on my canoe. I had glued them at the same time that I glued the inner stems. In order to fix this I ended up making new outer stems by laminating new strips. I suspect that if I had not glued the outer stems early on I could have used the strips I had since there is a fair amount of springback until they are glued.

[lamarkeiko]

I was hoping that someone else that has used plans would respond but it looks like that might not happen.

I didn't use plans for the Redbird we are making but used the offsets from Canoecraft. I checked the book for the Prospector and station 6 height is 23" plus 1/16" so what you are seeing there looks right.

I am assuming that since you purchased plans, these would be accurate. I can't find a reason for you to be out by 3/16".

At this point I would probably just shape the inner stem using the forms as they are right now. A lot of people don't use inner stems so you shouldn't need to worry about the slight compromise there. However, take any advise from me with a grain of salt. I'm just saying what I would do

Thanks for the thought frugal. I was also wondering if I just took that extra 1/4' from the base line of the stem if that would cause any problems I don't know about. By doing that, my stem fit shouldn't change. I think at this point I will wait a little longer to see if ther is anyone who has also had this problem.
Lamar

[Glen Smith]

If station 6 is the correct height, I would measure the thickness of the inner stems then remove the difference from the curved edge of the stem forms along the entire edge. So, if you are off by 3/16", remove 3/16" from the curved edge of the stem forms all along the curved edge. Then, if the stems you have already made don't fit properly, make some new ones.

With paper plans, the dimension can vary by as much as + or - 1/16" depending on the humidity but I cannot understand the 3/16" difference. :rolling eyes

Are your inner stems exactly 3/4" thick? Did you remove exactly 3/4" from the edge of the stem forms to accomodate the inner stems? CanoeCraft calls for 3 X 1/4" strips to be laminated together with thickened epoxy to make the inner stems. However, thickened epoxy always has a certain thickness to it so you would obviously end up with inner stems that are slightly thicker than 3/4". At least that is the way I see from what I have experienced. That would not account for a difference of 3/16" though.

[lamarkeiko]

Hi Glen,
I think I have discovered the cause of my problem. The stems I made are exactly 3/4", and did not expand in height from glueing. I got to thinking some more and decided to make a couple more measurements on my full size stem plans and mold plans. They both have a measurement dimension from base line to water line of 20 1/2". The plan of the molds does infact measure 20 1/2" , but the stem plan drawing measures 20 11/16". The stem plan drawing is 3/16" too high. I think the stem plan drawing was misproduced slightly out of scale. Now my problem is what to do about it. I think I will just cut my stem molds 3/16" shorter from the baseline so the top of the inner stems will line up with station 6. This way I do not have to make new stems. I don't believe there will be enough difference anywhere else to cause a problem, as long as I readjust my stem mold sheer lines to match the height of station 6. How does this sound?
Lamar

[Glen Smith]

First thing you should do is report the error to Bear Mountain Boats.

You could probably get away with cutting the excess from the base of the stem molds. Don't forget to reposition the sheerline and the waterline.

info@bearmountainboats.com

[ealger]

I measured my Bear Mountain Prospector 16' plans and station 6 is 23" exactly. The stem mold height is 22 3/8" at the edge. However, I moved the edge forward 1/2" to allow for the thickness of station 6 as my reference edge is toward the inside of the hull. This put the stem mold at 22 1/4" high.

If your stem plan height is really off that much, I would suppose that the shape of the stem drawing may be skewed out of shape.
Ed..

[Glen Smith]

Dimensions and lines can vary a bit depending on when the plans were published. The Prospector was "re-faired" in 1999.