Skagit 20 - Alaskan Bulkhead

[Lyle]

That is very nice work, I can finally see where you are going with your design.

[Skagit Hideaway]

Here's the port side outer shell, lower half, glued in place. Next,
some more putty and tabbing. With any luck the seam won't be visible. The extra length starts to give the boat a real, PT boat look, minus the torpedos.

[Helmar]

....middle (3) platform sections (1/4" thick) ready for gluing/filletting/tabbing.

That looks pretty slick.
Glad to see you made it onto the new forum system

[Skagit Hideaway]

....middle (3) platform sections (1/4" thick) ready for gluing/filletting/tabbing.

[Kelly]

The extension looks great! Nice work!

[Lyle]

That looks sturdy, and is some good looking work. I will keep watching, I'm interested how you are going to 'skin' the extension.

[Skagit Hideaway]

The transom is mounted on the extension. Only the first brace is tabbed to it so far. 6 more corners to go. The dark green looking stuff is milled fiber puddy/glue which I just love mixing up and smearing on 'cause it looks like cake icing. Once the tabbed areas are trimmed down (as foreground Left) and recessed 1/4", the three, 1/4" thick swim platform/top brace panels will sit between the 4 extenson braces. There will be 2 on the ends as well. Same thing on the underside, including airoglide grooves. When finished, it will look something like the Grady White euro transom.

[Skagit Hideaway]

Preliminary lamination of the extenson transom (there are no bubbles in it) - 2 x 3/4" marine plywood with 1708/roving/1708/roving/1708/1708 on front/back/sides - then the whole thing is encapsulated with a lighter, more flexible cloth - 2-1/2" thick total. It gets glued/tabbed to the 4 extension braces, tops, bottoms and side pieces, and ultimately to a 1/4" shell that goes around the outside of it and is tied in to the original hull. Same principle as the original transom - no bolts or screws holding anything on. Total extension weight est. 150lbs.

[Skagit Hideaway]

As I said, there are many other considerations related to b/l ratio, so I use the term "ideal" very loosely. You have never heard/read of the 3:1 ratio as being the rule of thumb, classic proportion, conventional wisdom, blah, blah, blah, beam to length ratio for small seaworthy powerboats? The Boston Whaler 22 Outrage has a 3:1 ratio I hear.

[Bflaherty]

[quote="Skagit Hideaway, post: 29822, member: 2454"]

To figure the ratio the other way:

Skagit 20 : 2.6
Skagit "22": 2.86
Ideal 22.5 : 3

Where did you come up with the "ideal" ratio of 3:1?

[Skagit Hideaway]

[quote="So the Skagit 20 is .385 - 13.3% larger than the ideal .3333... (1/3), and outside the +/- 10% range of safe deviation. OMG. Ha, ha. The 21' - 6" Skagit has a .348 ratio - 4% off the ideal. The ideal length would be 22' - 6".[/quote]

To figure the ratio the other way:

Skagit 20 : 2.6
Skagit "22": 2.86
Ideal 22.5 : 3

[Skagit Hideaway]

The 4 extension pieces are finally attached to the transom. The 1708/coremat/roving sandwich laminate is incredibly strong. You'll see many pictures of coremat failure online. This is due to using thick layers of it with insufficient resin absorbsion. A single 1708/2mm cormat/single 1708 laminate is amazingly stiff and practically indestructable. They have samples at Tap Plastics that are correctly done.

These "boards" have 4, 1708/coremat/1708 sandwich layers in them with some roving thrown in and extra 1708 on the ends. Huge overkill maybe, but I'm not going to need to worry about 180 hp tearing them up.

So the 19'-6" Skagit is going to be 21'-6" long. Some trivia: I know it's just a guideline, and there are many other factors to consider, especially for planing hulls, but, the length/beam ratio of the stock Skagit 20 is .385 - 13.3% larger than the ideal .3333... (1/3), and outside the +/- 10% range of safe deviation. OMG. Ha, ha. The 21' - 6" Skagit has a .348 ratio - 4% off the ideal. The ideal length would be 22' - 6".

I'll have to think of a name for this new Skagit 22 model.

[Skagit Hideaway]

Beginning of the extension's outer shell, Port side aft, which will retain the original hull shape, made by laminating a sheet of plastic stretched over the stern, Port corner of the hull.

[Skagit Hideaway]

I worked a deal with TAP Plastics (1 mile away) to match Burlington's price on their 1708.

reg. the transom picture above: the boat is listing to starbord on the blocks.

[Skagit Hideaway]

Here's the inside of the transom before filling the cut-0ut. Motor mount, hydraulic cylinder mount, and kicker mount holes plugged and bored. The stringer ends were chopped back ca 8", the new transom filletted/tabbed in, and then new stringer ends formed over styrofoam cores, overlapping the old stringers 6" or so. Now that I'm adding the hull/outboard extension, I'll be extending all the stringers to the transom, as per the center one. The original deck support pieces at the transom consisted of a short 2x4 on the inside edge next to a piece of 1/2" plywood that extended to the side of the hull. As these corners were going to be steps for getting in and out of the boat (there were going to be corner seats built into the transom well.) I glued in 3 layers of laminated 1/2" marine ply that extend past where the side, extra freeboard thing meets the deck, on both sides. That fimed up the whole rear end and deck immensely. This transom ended up being 2-1/2" thick, which was 1/8" larger than the old 1972 100hp Johnson motor can handle. I notched the edge accordingly. Now all that is filled in.