Core Material for crown on Roof Recore

Offshore121

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I agree with everything said on this post and would add this. I recently faced a tough decision on my top. It was made by Terry and he used scored divylcell. I'm not positive as to the thickness but can't be more than 3/4".

I was going back and forth on the top as head room is minimal. I'm not sure about the fit of the 6.7L cummins, angle of install even with the ZF280A. It seems it sits quite high in the bilge. I have about 5" of clearance from the bottom of the oil pan to the drip pan. Not complaining about this but it does raise the deck a little to avoid an engine box. As it is right now I barley have 11" from the projected waterline to the bottom of the turbo.which I will have to deal with. Not to derail the post with my problems but I have decided to go with it as is for now as I will not have the time to redo the top even though this would be the perfect time to do it.

Back to my top as mentioned above it is scored H80. It does have a definite "oil can" effect walking on it ever so carefully. And I would not consider walking on it without supporting the aft portion. So, if I were to do this I would probably lean towards 1" foam. As it makes seams and edges much easier to deal with on a one off project It is simply a matter of choice as I have used a lot of both carbon core and foam as each have it's advantages. I would avoid the scored for a couple of reasons.any solid foam or honeycomb will readily take to whatever camber you decide on.and, would be much stiffer than scored. You would also be using albeit slightly less resin filling in the "cracks".

And, as time intensive as it would be, I would build a mould to properly lay up and achieve the look and shape you want. I would also add hot coating the core before applying it to the first layers of glass. I ground the gunnels to prepare for some coaming in the cockpit and came across quite a few areas of "dry" core with no resin/glass contact. In fact I would hot coat the core and spread a slightly thickened resin before placing the core in the mould. And yes Merton's sells scored and non scored H80 as well as coosa and is a great source for advice.Just my two cents

What's the rough overall size of your roof? my current balsa core roof had a little flex to it when walking on but also had a winterback so its supported.
 

BillD

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What about using oversized aluminum backing plates for bolt thru items. To help spread the load out.
would a nida or divinycell still be ok? Still decoring holes like normal practice.
Offshore,
I noticed in your post you are asking about how the 6.7 will lay in the hull.
My 25 T Jason has a shaft angle of 7 degrees. 7 degree angle seems to be the "factory spec" angle for the DEs.
The ZF280 gear is a 7 degree down angle gear.
The 6.7 in your 35 TJ should be just about zero bubble with a level on top of the engine after install.

For what it's worth,

Bill D
 

Islandlure

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Sounds like you just confirmed the layup schedule we are talking about too..

How did you go about glassing both sides in this method?

Did making the arc on the honeycomb give you any trouble, did you score it or anything?
I made a table with MDF and heavy release was then just laid up my 1708 and mat, put core down, and lots of rocks and weight on the core to keep everything tight. After that kicked, I did the same on the underside. Once everything dried I popped it off the "mold" I made. I had some imperfections from screws and some seams but some 80 grit took care of that once we got it up on the boat. Let me know if have questions.
 

Offshore121

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I made a table with MDF and heavy release was then just laid up my 1708 and mat, put core down, and lots of rocks and weight on the core to keep everything tight. After that kicked, I did the same on the underside. Once everything dried I popped it off the "mold" I made. I had some imperfections from screws and some seams but some 80 grit took care of that once we got it up on the boat. Let me know if have questions.
Your roof look a lot larger than mine will be, any flexing from the nidacore after layup? how did you finish the edge of the roof?
 

Offshore121

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Offshore,
I noticed in your post you are asking about how the 6.7 will lay in the hull.
My 25 T Jason has a shaft angle of 7 degrees. 7 degree angle seems to be the "factory spec" angle for the DEs.
The ZF280 gear is a 7 degree down angle gear.
The 6.7 in your 35 TJ should be just about zero bubble with a level on top of the engine after install.

For what it's worth,

Bill D

BillD I think you meant to reply to going4broke. My 31JC has a cat in it.
 

Islandlure

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Your roof look a lot larger than mine will be, any flexing from the nidacore after layup? how did you finish the edge of the roof?
I decored the edges with a razor knife and flat screwdriver then packed it with some HD putty mixed with some fibers the hit the edge with a router bit.
 

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Lobster.mike

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Plenty of great tips and ideas here—really great discussion. I’d just like to add that if going with Coosa it’ll be harder to keep the shape since it’s rather stiff. On a roof of that size it should be cut into wide strips then ground and fitted. Always take the “sheen” off with some light sandpaper before glassing. There’ll be more work in prep and fairing. Joe at Mertons has foam as well. That’ll take the shape much better. I’d stay away from the balsa.
 
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