The 18 Foot SeaSled

[Darkzillicon]

At the suggestion of the other SeaSled guy @DogCavalry I have made a new thread for building updates.

I purchased a copy of the 1950s? Boatbuilder SeaSled design called “seajet” lofted my frames and made some modifications. The original design said it would be planked with 3/8” ply and my intention is to put 1708 inside and out.

the frames, stems, and most of the stringers are in place. I chose to make the transom out of coosaboard 26 and it’s all held together with epoxy as I’ve tried to keep any metal fasteners to a minimum. Even those fully encapsulated.

I am currently as of a few hours ago gluing the “planking” to the framing on top of the gunwales and I typically prime both pieces of wood with regular clear epoxy then apply my thickened epoxy to join it together as shown.

 

[fallguy]

What is your transom angle? Pictures are so deceptive for me.

 

[Darkzillicon]

What is your transom angle? Pictures are so deceptive for me.

I don’t remember exactly but it’s a 24.5” transom 6” off the vertical at the top.

I want to say 12ish degrees, it’s been awhile since I worked on that area.

 

[DogCavalry]

13.75°, from the trigonometry

 

[Darkzillicon]

13.75°, from the trigonometry

it’s in that ballpark. I can give an exact but I’m in the process of modifying my “asbuilt” plans to reflect any small changes that I made. It’s probably a waste of time, but it’ll help when I do my weight study and when I need to calculate areas for doing flotation foam.

 

[fallguy]

What engine uses a 24.5" transom? Sorry, but something seems odd to me. And it is probably all camera angles, so forgive me. What is the black area and material?

Was this boat featured in a magazine? Where did you get the drawings?

 

[Darkzillicon]

What engine uses a 24.5" transom? Sorry, but something seems odd to me. And it is probably all camera angles, so forgive me. What is the black area and material?

Was this boat featured in a magazine? Where did you get the drawings?

I think i mentioned this previously it was in a magazine called "boatbuilder" very prolific designer who built lots of plywood craft on some lake in the Midwest. I found the PDF files so I don't know the exact provenance of the design.

Per the original drawings (I have made some small modifications hence why I am making the "as-built plans")there is a cutout down to 18" to allow for an outboard. I chose to omit this cutout as I could always cut down the transom at any point and I assumed that when I get to rigging the boat, I may choose to use a 25" shaft outboard which would allow me to have a higher cutout. The Black Material is Coosaboard Bluewater 26 and the inner surface has a single layer of 1708 and west systems epoxy. Wood transom framing is laminated to the Coosaboard.

 

[fallguy]

Okay, so the black is the transom; that helps me a ton, somehow I was going the other direction.

 

[Darkzillicon]

This isn't gospel this is a 3d model I designed before starting construction... it's mostly accurate but the heights of some of the elements have changed. The scantlings are beefed up in the rear 3 frames... but broadly speaking this transom angle should be good enough for government work.

 

[fallguy]

I'm a little surprised at the transom design.

What is your intended power?

How thick is the coosa?

To get it to the same rigidity as 1" plywood will be more than 1x 1708.

 

[Darkzillicon]

I'm a little surprised at the transom design.

What is your intended power?

Per the plans she needs 1.5" of total plywood thickness. I wanted to do a 1708/Coosa/1708/Coosa/1708 Sandwich. But the Coosa is fairly stiff. and I do have that 2x4 back there. But yes as it currently stands the transom is a bit flimsy, also this is undecided.

Per the plans up to 90hp. so my original idea was a Yamaha F90. However, i am very open to running a diesel with a large screw to help with the ventilation and/or if I want to get exotic an Arneson drive. One of the reasons that I want to finish the "as built" plans is so that I can do some computer work to figure out what will work best for power. In the meantime, I do need to get the rest of the planking done. from what I understand in plywood she was a 500 pound boat.. so if i assume 1000 pounds with 90hp that would give me 40mph and 7mpg fuel burn on that Yamaha but again we are getting real world results from @DogCavalry so i will try to learn from his mistakes/wisdom.

 

[fallguy]

So, right now, you have 1708, 3/4" coosa, 1708?

 

[Darkzillicon]

So, right now, you have 1708, 3/4" coosa, 1708?

1708 on the inside, 1/2” coosa26 outside. Additional lamination will be on the back of the boat. I think you can see from the photos I don’t have room to do it right now. Lol it’s up against the wall.

 

[fallguy]

Yeah, that ain't gonna be a transom as is.

The compressive strength of coosa for bolting on OB is about 1/7th that of plywood. And the flex is about 5x as much, so coosa bw requires lotsa help from the laminate..

 

[Darkzillicon]

Yeah, that ain't gonna be a transom as is.

The compressive strength of coosa for bolting on OB is about 1/7th that of plywood. And the flex is about 5x as much, so coosa bw requires lotsa help from the laminate..

do you think I should give up on the alternating layers and just make it a thicker Coosa board and then do my lamination entirely on the outside or do you like the idea of the alternating sandwich?