Recently bought a 2020 JP SLW board which has a concaved area on the deck around the mast base. Mast base became loose and separated from the board on an early outing. I assumed I hadn't tightened the base sufficiently and since then have been tightening as firm as I can. When de-rigging on last outing I noticed the base had loosened and was only finger tight. Has anyone has this issue on a board with a concaved deck? I assume it has something to do with screwing a flat base on to a concave surface? Any tips or tricks? Can you buy a special base for concave decks?

Perhaps you could try a 2 bolt deck plate (like the Chinook) if you are worried about it coming loose.

OW, had a similar experience on my Rocket. Usually i use 2 bolt. But to get mastbase where i needed reqd single. Cranked it up nice n tight. Sailed for 30 min or so.Went to tack n felt something loose. Mast base was about half a thread from disconnecting.
Maybe you could remove the locating disc so it doesnt spin so easily? So corners/edges of mastbase actually touch the deck. Will be checking mine every few runs until i find a solution.

Try emailing JP via the contact page on their website and ask them what bases they use. It will highlight to them a potential issue.
I asked them a question about a board last year and someone responded with 24 hours with a detailed answer.

Only had a mast base come loose on me twice. Im pretty sure what happened is the T nut on the mast base grabbed at the top of tbe T nut, then slipped later under force. But it was quite a drastic change in tension. Not the tight to finger tight change you mentioned.

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Roy said..
Perhaps you could try a 2 bolt deck plate (like the Chinook) if you are worried about it coming loose.

I found this to be the cure when this occurred to me. Streamlined make a nice 2 bolt also.

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Orange Whip said..
Recently bought a 2020 JP SLW board which has a concaved area on the deck around the mast base. Mast base became loose and separated from the board on an early outing. I assumed I hadn't tightened the base sufficiently and since then have been tightening as firm as I can. When de-rigging on last outing I noticed the base had loosened and was only finger tight. Has anyone has this issue on a board with a concaved deck? I assume it has something to do with screwing a flat base on to a concave surface? Any tips or tricks? Can you buy a special base for concave decks?

I remember I had that issue when I first got my isonics..I think it was an older style mast foot.
I bought a modern one and that solved it..

The current Duotone deckplate comes with a rubberised pad that seems to grip my board well.
That said, I've never had any deckplate slip on me - and I use single bolt ones, to get the full mast track range. .
Which deckplate are you using?

Is the non-slip on your new board perhaps a bit coarse - and is still wearing in?
The other thing that can happen with a new board is if the box top was sanded excessively before lamination during production. That can mean the single bolt of some deckplates might hit the bottom of the track before the pressure plate tightens properly. Look for telltale bolt marks at the bottom of the track, like a circular dent.

I would add however, that I know of other sailors with recent JP boards and they have not reported this problem. The deck dome around the track did not look extreme to me.

The second issue that happens is when your bearings are not working properly. So the mast rotates in normal use but unscrews the deckplate.

A normal deckplate has two bearings. I have seen dubious posts online where people recommend using a line from the sail tack to the U/J as a safety device - and that is a dumb thing to do as it locks off the upper deckplate bearing, causing this problem. .
There should be a rotating bearing either side of the U/J.

I've found the T nut can catch somehow on something inside the mast slot so I'd do it up tight only to find oud a couple of runs later the mast was at the front of the track.
Now I jiggle the mast base around a bit and lift it by hand when tightening and haven't had a problem since.

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Basher said..
The second issue that happens is when your bearings are not working properly. So the mast rotates in normal use but unscrews the deckplate.

A normal deckplate has two bearings. I have seen dubious posts online where people recommend using a line from the sail tack to the U/J as a safety device - and that is a dumb thing to do as it locks off the upper deckplate bearing, causing this problem. .
There should be a rotating bearing either side of the U/J.

This happened to me, the unscrew part, not the dumb bit.

Thanks for the replies. I have a two bolt base, haven't used it for a while but will fit it, should solve the problem. Basher, this is the base I've been using. I actually used it again today and it didn't come loose, but I only sailed for about an hour.

Similar issue with longboard skate. I used... well you guessed it, rubber tube of course!

Could it be because the deck is concave it feels like you have it tight but thats only at the edge, at the bolt its not as tight as it should be?
Does the UJ rotate freely around on the base and the mastcup?

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Manuel7 said..
Similar issue with longboard skate. I used... well you guessed it, rubber tube of course!

Sorry, excuse my ignorance, what do you mean?

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PhilUK said..
Could it be because the deck is concave it feels like you have it tight but thats only at the edge, at the bolt its not as tight as it should be?
Does the UJ rotate freely around on the base and the mastcup?

Possibly. Yes, no impedience to rotation, all normal.

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Orange Whip said..

Manuel7 said..
Similar issue with longboard skate. I used... well you guessed it, rubber tube of course!

Sorry, excuse my ignorance, what do you mean?

You mean you hit the water WITHOUT one of these???

Thanks! Yes, what happens is that the plastic of the base starts to lose its shape. It slowly bends from the tension. When you take it out you'll notice that it's slightly bent so the friction weakens and it gets loose.

Solution is either tightening it harder in the first place to accommodate later bending or use a piece of inner tube which will increase friction between plate and deck or tighten after some time within the session or use a 2-bolt base :) !

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Manuel7 said..
Thanks! Yes, what happens is that the plastic of the base starts to lose its shape. It slowly bends from the tension. When you take it out you'll notice that it's slightly bent so the friction weakens and it gets loose.

Solution is either tightening it harder in the first place to accommodate later bending or use a piece of inner tube which will increase friction between plate and deck or tighten after some time within the session or use a 2-bolt base :) !

Cheers. No bike tubes lying around at my place so bought a metre of 1.5 x 100 rubber from Clarke rubber for $8, enough for about 10 bases, worked a treat today.

Good deal! I was lucky enough to find a dead truck tube on the beach, years of supplies :D ! I did also go dumpster diving at the local moto shop. The beauty about it is even punctured they still work for us :)