PH15/XF20 Tunnel Question

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txjm
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PH15/XF20 Tunnel Question

Post by txjm »

I was reading a relatively recent post on putting the 3” fillet in a tunnel.
It seems like a lot of materials to get to that radius. Would it be good practice to do the lamination of the inside and outside of the tunnel assembly and then use a foam or marine ply “filler” to eliminate the amount of resin and flour used when putting in the radius?
Second, the post I was reading, it appeared that the poster radiused the outside of the tunnel. It looked great but does it provide any advantage? I was thinking that it makes a big crevice between the top of the tunnel and the stringers.
Chip

Matthew Anderson
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Re: PH15/XF20 Tunnel Question

Post by Matthew Anderson »

Thank you for the kind words.

I too was initially looking for a way to reduce the amount of filler for the 3” radius. Wrap a 6” pvc pipe with glass and epoxy to make a fiberglass tube, cut into a quarter round and install, plus several other ideas. DONT OVER THINK IT. Build it just as the plans describe. It turned out great plus it is very sturdy. There will be a lot of forces taking place in tunnel as water is compressed through it at over 30mph.

The top of the tunnel box has a 1/2 radius of wood flour and epoxy to allow the 12oz bias tape to lay flat without bubbles over that seem. Once the boat is flipped I will glue in the stringers. Should be fairly simple. The tunnel box sits snugly between the stringers now that are not permanently yet, just resting in the molds. I’m raising the sole of my boat by 1 1/2” by making my stringers taller. The void from the top of the tunnel to the underside of the floor decking will be filled with foam as will most of the rest of the sole, minus the fuel tank area.

I hope this helps. Good luck and #Buildon.

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Re: PH15/XF20 Tunnel Question

Post by jacquesmm »

And yes, you can use a foam filler for that radius but use marine foam, not insulation foam.
The BBC buoyancy foam will work.
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txjm
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Re: PH15/XF20 Tunnel Question

Post by txjm »

Thanks for the responses.
Chip

txjm
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Re: PH15/XF20 Tunnel Question

Post by txjm »

I am resurrecting this thread.

WOW these boats are structurally a tunnel with a boat built around it. With the layup and the attachment to the stringers and the lamination to the bottom, the tunnel should be indestructible.
I do have three questions?
1 What radius should be where the bottom transitions to the tunnel? I assume a 1/2" radius on the sides and a really big smooth radius on the front and where the 3" radius meets the bottom in the front.
2 I saw one person laminate the tunnel to the bottom with a rectangular piece of glass. He did not notch the glass at the front corners. I like this, how hard is it to get the glass to lay down when laminating it in place?
3 Would it be of any advantage to sharpen the transition of the sides of the tunnel to the bottom of the boat in the last foot or so of the tunnel or is it best to have a 1/2" radius all the way back?

Thanks
Chip

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Re: PH15/XF20 Tunnel Question

Post by TomW1 »

txjm wrote: Sat Oct 02, 2021 4:45 pm I am resurrecting this thread.

WOW these boats are structurally a tunnel with a boat built around it. With the layup and the attachment to the stringers and the lamination to the bottom, the tunnel should be indestructible.
I do have three questions?
1 What radius should be where the bottom transitions to the tunnel? I assume a 1/2" radius on the sides and a really big smooth radius on the front and where the 3" radius meets the bottom in the front.
2 I saw one person laminate the tunnel to the bottom with a rectangular piece of glass. He did not notch the glass at the front corners. I like this, how hard is it to get the glass to lay down when laminating it in place?
3 Would it be of any advantage to sharpen the transition of the sides of the tunnel to the bottom of the boat in the last foot or so of the tunnel or is it best to have a 1/2" radius all the way back?

Thanks
Chip
The radius should be fairly small as possible from as from the front to the the transom so the water flows off it cleanly, an 1/8 would about ideal depending on the amount of fiberglass you have to use, but keep it as small as possible.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

txjm
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Re: PH15/XF20 Tunnel Question

Post by txjm »

Thanks Tom

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