Questions on Petrel Strongback and skin finish

Submitted by chrisail1946 on Sun, 03/31/2019 - 12:41

Starting build and have a few questions of PTPlan sheet 2 of 10, 2005 nick shade drawing for the Petrel.  

1. Is there a video or photos of the SB and partial build? How about links to a few  recommended instructions. I'm new to this and appreciate any help. I am working from and very appreciative for the build videos of the Petrel Sport, but it's SB is oriented horizontally along the 4" axis and the PTPlan is designed on a vertically oriented SB.

2.Is it necessary to taper the SB at both ends,  from 4" height to about 3" , ie between the last frames with thru holes for the SB and next outboard frame? The sheet 2  shows a SB tapered from 4" to an unspecified dimension at the ends, where it contacts frames #3 and #15.

2. Is there a recommended finish for the interior of the skin? I will review the video of the Petrel Sport for this. I assume the interior surface of the strips need to be sealed from exposure to water.

Thanks,

Chris

Chris, 

i am not sure what your abreviations mean?  is SB mean the Strong Back?

if you could clarify....that would be great.

i have built several of nick's design....the petrel and the night heron...but not the petrel play.

that said, on the inside skin, 6 oz e-glass would be the 'standard' layup.  you can go as light as 4 oz.   several of the areas on the inside would need some more material....around the cockpit and coaming areas.  either of Nick's book on kayak building, "Building the strip planked boats" or 'The Strip-Built Sea Kayak" ,  will give proposed layups for internal and external glass and are a very useful complement to the videos and plans.

h

 

JohnAbercrombie

Sun, 03/31/2019 - 19:32

It's  'wood core composite' construction, so be sure to follow Howard's advice.

Wood strips need epoxy/fiberglass on both sides to provide the strength and stiffness required.

In a stitch and glue plywood boat you can 'get away with' just coating some of the surfaces with epoxy (or even just paint), without glass, but glass on both sides is a lot stronger.

The interior glass-epoxy surfaces that are exposed to UV (cockpit) need varnish for UV protection if finished clear.

Howard,

Yes, SB stands for Strong Back. Sorry for the confusion.  Also I now understand that (1.) there is to be a layer of glass on the interior of the skin, so the skin is a sandwich construction of  3 layers: glass/wood/glass and  (2) I could use Nick's book.  

Can you comment on my question 2 ?

"2.Is it necessary to taper the SB at both ends,  from 4" height to about 3" , ie between the last frames with thru holes for the SB and next outboard frame? Sheet 2 of the plan shows a SB tapered from 4" to an unspecified dimension at the ends, where it contacts frames #3 and #15." I don't see a need for the taper.

Thanks for your help.

Chris

 

while i don't have the strongback plans for the Petrel Sport, what you are describing looks very similar to  the petrel strongback.....both ends taper.

the reason for the taper may not be clear until you think about this in three dimensions.  the boat gets pretty skinny in the ends..and the end curve up.  so i think, you would find, that if you did not have the taper, the strongback would interfere with the stripping.

looking just from a side elevation, this would not be obvious.  and when they give you the sections, they have already taken into account the taper....

i bet if they did not have the taper, you would see the the strongback coming through the side of the bottom of the hull where it was not cut back.

i hope that helps to explain it.

howard

JohnAbercrombie

Tue, 04/02/2019 - 13:26

You could always build the boat with a 'traditional' (external) strongback, though it would be more work aligning the forms.