Hey,

I am in the process of converting an older single into a twin fin.

Just looking for some data out there, distance between the fin boxes (center to center), distance from the tail.

My board is very similar, dimension wise (at 300mm, 2000mm, volume, width, length, etc...) to the Patrick Diethlem Wide Trailer Wave 85L. I would be interested to get the measurement of the fn boxes on that one. They seem quite far appart, like 200mm for the twin boxes which is more than the "rule" about 140mm appart I heard...

Anyways, any input, data would be greatly appreciated!

Cheers

Not too close to the rail, then they can cavitate bad unless you cure that with some cant - which is a black art that seems only Hoops has got right.

about 17- 20cm apart seems safe

distance from tail is really hard, depends on rocker and all sorts.

If all you are trying to do is loosen a single, maybe make it a thruster with a little toe on sideys and run a much smaller centre fin. Less surgery and easier to get right. Just thoughts....

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Mark _australia said..

Not too close to the rail, then they can cavitate bad unless you cure that with some cant - which is a black art that seems only Hoops has got right.

about 17- 20cm apart seems safe

distance from tail is really hard, depends on rocker and all sorts.
If all you are trying to do is loosen a single, maybe make it a thruster with a little toe on sideys and run a much smaller centre fin. Less surgery and easier to get right. Just thoughts....

Thanks for the input Mark, trying to copy a Trailer Wave at this stage, I'll give it a shot at 190mm appart, will update once it's done with measurement and all as well as a verdict on the water

Nah don't base it on mine, that was just my guesstimate thoughts. Ask Rider5 what he reckons - where are ya Mike?

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Mark _australia said..

Nah don't base it on mine, that was just my guesstimate thoughts. Ask Rider5 what he reckons - where are ya Mike?

Well, scaling the Trailer Wave Wide 83L, I got a distance of 190mm centre to centre, so not far off...

Agree with Mark will be much easier to convert to tri fin, at worst if it doesnt work (which it will if you get toe and dimensions right) then blank them off and you will have the same board as a single fin as before, most boards built as singles dont convert to twins or quads due to shaping methods or design suited to one or the other, good luck!

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Zachery said..

Agree with Mark will be much easier to convert to tri fin, at worst if it doesnt work (which it will if you get toe and dimensions right) then blank them off and you will have the same board as a single fin as before, most boards built as singles dont convert to twins or quads due to shaping methods or design suited to one or the other, good luck!

Cheers for that, will still risk it! I've seen an old thread of my board modified as a twin, apparently it went well, just could get the dimensions of the guy who did it.
As you said, I ll blank the fin boxes if it doesn't work... Board is worth nothing anyways so not too risky

MAke sure you sort out the divinicyl requirements around the boxes and dont use "Shapers" US boxes use windsurf specific there to shallow for windsurf fins.

I did it with a fanatic 104 into a quad but messed by not enough support around the boxes and they all came loose after 3 months - it worked well as a quad though - its back to a single fin now and looks like its been beaten with an ugly stick - but still goes ok

Enjoy

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russh said..

MAke sure you sort out the divinicyl requirements around the boxes and dont use "Shapers" US boxes use windsurf specific there to shallow for windsurf fins.

I did it with a fanatic 104 into a quad but messed by not enough support around the boxes and they all came loose after 3 months - it worked well as a quad though - its back to a single fin now and looks like its been beaten with an ugly stick - but still goes ok

Enjoy

Yep, got the chinook fin boxes. What did you use around as support. I don't have any sandwich PVC sheets so was thinking of using a combination of thin balsa and carbon, should provide enough support.
I have a fanatic allwave 85l, so glad it worked on yours!

I used nothing and became loose after 3 months - someone here might have a good system other than divinicyl but I have no idea - I was a little out of my comfort zone doing this - god fun though

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Mark _australia said..

Nah don't base it on mine, that was 1o my guesstimate thoughts. Ask Rider5 what he reckons - where are ya Mike?

Here I am Mark

Twin fin boxes are usually around 13 to14cm apart and on a pintail about 17 to 19cm from the tail if the rear footstrap plug is say 25cm from the tail. Where your back foot goes affects the load you put on the fins.

The boxes need to be secured to the deck eg pvc or a hollow carbon batten filled with light weight filler and resin front and rear of box.

Ive converted many singles to twins then to quads. skip the twin conversion and just make it a quad and do not toe in the front fins as other self made forum experts recommend.