Shaping Prospector's stems

[edmontonian]

Hi gang,

I have finished the initial shaping of the stems for the strip glue up. In order to make a tight fit for the strips, I actually had to remove half of the plywood on the forms, leaving 3/8 of plywood behind. Is this normal?
Also, the diagrams from Canoecraft suggest profiles A-E being slightly different as one moves along the stem. My results suggest a narrow profile closer to E and D almost the whole way along. I am taking less plywood off as I move along, but I am caused to wonder if I am missing something. Suggestions are appreciated.

Edmontonian

[frugal]

When you made the forms for the stems did you take off the 3/4" for the inner stem?

[edmontonian]

Hi Frugal,
Thanks for your reply.
I did not remove any material from the stem. I think I plotted the table of offsets on to the ply and neglected to remove 3/4".
Do I simply cut this 3/4" amount off of the straight edge attached to station 6 then re-make the stems? Please let me know.

Edmontonian :embarassed

[frugal]

Cutting 3/4" off the flat side of the stem forms won't work. You will find that the inner stem is also too high.

What worked for me was to use a guage to mark a line 3/4" inside the curve that was cut (from the offset table) and cut the stem forms again.

There is a minor note on this in Canoecraft that I don't think is very clear. luckily I noticed this after I cut the stem forms the first time and looked at the photos more closely.

[ealger]

Edmontonian, to be clear; you have set the stem form against mold 6 and you have layed up and glued the inner and outer stems?

If this is the case, the stem mold, where it meets station 6, should be 3/4" below station 6.
when you add the inner stem to the stem mold, the top of the stem should be flush with the top of station 6.

Does this sound like what you have?
Ed...

[edmontonian]

Hi ealger,

Yeah, I glued up the stems, then mounted the inner stems to the molds. Both bow and stern fit flush with the top of station 6.
I just cannot explain why I am taking off so much ply during fitting. I must have done something strange.
I think I will chock this one up to learning. I'll re-plot, re-cut, and re-steam the stem molds and make a comparison. :confused
I just finished getting the replacement stem molds plotted and re-cut to plywood. In comparison to the originals, it looks like I did remove 3/4" from the bottom edge of the stem molds. I cannot recall doing this when I made them. I must have been tired!

In order to re-fit these corrected stem molds to the strongback, would it be best to use the string line to align everything again? Or worse, will I need to remove all the stations and mount each one again?

edmontonian

[ealger]

You say that the inner stem sits flush with the top of station 6. You do mean that the tops of both the stem and station 6 are flush? Not that the bottom of the stem is flush with the to of station 6?
If you "took half of the stem mold, leaving 3/8"", then your stem mold is 3/4" thick. If this is the case you may not be that far off. I say this because usually, the stem mold is made from 1/2" material and because the Prospector is "cheeked", it will fair quite close to the stem mold even cutting into the mold on the upright forward edge.

The faired inner stem will fair to about 1/4" or slightly less perhaps (on the forward upright edges).

Giving us a picture might help.
Ed...

[edmontonian]

Hi ealger,

Yes I did use 3/4" ply for the stem forms. I had some 3/4" around, so I used it. Now I know why 1/2" would have been the better choice.
I have now steamed new stems using walnut outers and cedar inners on 3/4" plywood, again. It looks like I will be going through the plywood removal process one more time in order to fit the strips to the stems.
The good news is, the new offsets I plotted are per Canoecraft's instructions, minus 3/4" for the stem thickness. Thanks to frugal for this reminder, this correction has been made..
Next build, everything will be 1/2" plywood, stem forms included. Thank-you for this advice on plywood material selection for the stem forms.
The inner stems now line up perfectly flush to the top of station 6. They did before this whole thing began, but I had incorrectly removed a 3/4" portion of the stem form edge which rests on the strongback, only reducing the height of the stem form.

I have definitely learned from you guys.
Thanks again all.

edmontonian :eyebrows

[ealger]

Hey Edmontonian, glad you're making progress.
I forgot to ask about the edge of the stem form which contacts mold 6: When the stem mold is plotted, the edge towards mold 6, is assumed to be on the "reference" edge of mold 6.
This means, if the reference edge is toward the inside of the hull (away from the stem) you must compensate for the thickness of the mold 6 material and remove that from the stem mold.
If this is not done, then the fair line to the stems will not be correct.
Also the position of mold 7 is fairly critical on the Prospector. A 1/2" either way will affect the fair inthe cheek area.
Ed...

[edmontonian]

Hi ealger,

I have confirmed that the reference edge of the stem form is the same as the outermost edge of station 6. It's looking good to go very soon!
If I move the station 7 half molds further forward, less cheek is the result. Does this reduced cheek at bow and stern equate to less material being removed from the stem?
Or does this move further complicate fairing up to the station 7 half molds and on to the stem?

edmontonian :smile

[ealger]

Moving station 7 does have an effect on fairing all the way along, bottom to top. Placing the station 7 form, to the plan point, preserves the designers rendition of course.
However, this doesn't prevent you moving or even changing the shape to suit your artistic view. Placing scrap 1/4" strips along the faired line would give you an idea on what the result would be. Take your time to do this! Once you start stripping, it's too late to make drastic changes.
Of course this examination on fairing goes for all the mold stations. Any deviation from a fair line gives the builder "extra" challenges in the stripping process. You'll have enough of those as you go along without worrying about your initial setup.
I like to use MDF for my forms because the material sands easily.
Ed...
http://s12.photobucket.com/albums/a237/ ... spector16/

[edmontonian]

Hi Ed,
When I replace the old stems and forms for new, do you think I will need to re-align all stations with the string jig or is just a stem form re-alignment/ install OK? Other than the stem forms attached to station 6, nothing else moves.

edmontonian