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Old 15 April 2008, 18:21   #21
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The deck of your Destroyer will be approx 20mm thick. Find the thickest screws possible and get a few of these. For your main fixing screws use one size thinner. This gives you the opportunity to fit a thicker screw should you strip a thread while tightening. Plywood isn't always as homogeneous as one might like.

I have no problem with you using sikaflex but I wouldn't use it.

What no one has mentioned and is essential if you want a good job done, is to ensure the area you are jointing to is degreased, the seat base is degreased and also the self tappers are degreased. I put them into a tin of thinners and agitate it with a wee paint brush then tip them out onto a rag or bunch of paper towel. Make sure your drill isn't greasy or oily and, because you're screwing into plywood, your pilot drill needs to be the same size as, or very slightly smaller than, the root diameter of the self tapper.

I don't know what your seat flange is like but you need to drive the screws in nice and square to the deck. I'm presuming you've got holes in your set flange. To ensure accuracy, place the seat in position dry and, using the same drill size as the flange holes, drill into the deck at one corner just enough to make a depression. Move the seat and pilot drill this hole. Put the seat back and fit a screw but don't tighten it enough to stress the thread it makes. Align your seat and do the same process in the diagonally opposite corner. Now you can drill the depressions through all the other flange holes and be sure they are well aligned. Remove the seat, pilot drill the holes, brush away all the swarf, degrease again to be sure, skoosh sealer down every hole, apply the sealer to the flange and screws and fit them being careful not to overtighten them.

For sikaflex, Richard's recommendation for masking around the area is very good. Sikaflex is blacker than black....provided you buy black stuff, of course.

I personally think self tappers, if done well into good material, are seriously strong.
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Old 15 April 2008, 19:00   #22
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Quote:
Originally Posted by jwalker View Post
The deck of your Destroyer will be approx 20mm thick. Find the thickest screws possible and get a few of these. For your main fixing screws use one size thinner. This gives you the opportunity to fit a thicker screw should you strip a thread while tightening. Plywood isn't always as homogeneous as one might like.

I have no problem with you using sikaflex but I wouldn't use it.

What no one has mentioned and is essential if you want a good job done, is to ensure the area you are jointing to is degreased, the seat base is degreased and also the self tappers are degreased. I put them into a tin of thinners and agitate it with a wee paint brush then tip them out onto a rag or bunch of paper towel. Make sure your drill isn't greasy or oily and, because you're screwing into plywood, your pilot drill needs to be the same size as, or very slightly smaller than, the root diameter of the self tapper.

I don't know what your seat flange is like but you need to drive the screws in nice and square to the deck. I'm presuming you've got holes in your set flange. To ensure accuracy, place the seat in position dry and, using the same drill size as the flange holes, drill into the deck at one corner just enough to make a depression. Move the seat and pilot drill this hole. Put the seat back and fit a screw but don't tighten it enough to stress the thread it makes. Align your seat and do the same process in the diagonally opposite corner. Now you can drill the depressions through all the other flange holes and be sure they are well aligned. Remove the seat, pilot drill the holes, brush away all the swarf, degrease again to be sure, skoosh sealer down every hole, apply the sealer to the flange and screws and fit them being careful not to overtighten them.

For sikaflex, Richard's recommendation for masking around the area is very good. Sikaflex is blacker than black....provided you buy black stuff, of course.

I personally think self tappers, if done well into good material, are seriously strong.
Think the 1 1/4 inch x size 10 self tappers should be ok. Whats below the 20mm deck thickness is it just a big V hull. If the self tappers come through the deck below a small bit is it ok? say if the self tapper goes in 25 mm or so. Or should i get a shorter self tapper.
Humber suggested 1 1/4 inch and then when they sent on instructions for fixing a console to deck it stated 1inch self tappers. I will have washers and the flange also so that will take up a few mm of length. Washers?
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Old 16 April 2008, 06:49   #23
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Think the 1 1/4 inch x size 10 self tappers should be ok.
Given that they need to go through the flange and that the pointed tip does very little then 1" seems about right.
Quote:
Whats below the 20mm deck thickness is it just a big V hull.
In the centre section there is nothing. The hull has two full length (almost) longitudinals. They start at the transom where the support knees are and they are (should be ) parallel.
Quote:
If the self tappers come through the deck below a small bit is it ok?
Yeh, I reckon. I held everything to the deck of my Destroyer using self tappers and silicon for a seal, 50gallon stainless tank, console, highbacked seats, hold-downs for ratchet straps and bracing for a 7ft high frame. Nothing came loose and the hull didn't leak.
Quote:
I will have washers and the flange also so that will take up a few mm of length. Washers?
As I said, I don't know your seat flange but if it's 6mm or so thick and properly moulded it will be strong and I'd not be using the washers.
Raised head screws are good because the countersink locates the screw into the flange and helps prevent any sideways movement. The slight domed head looks good and prevents the sharp edge that countersunk screws have if they stand a little proud.
I used a screw spacing of approx 70ish mm for my seats. If you need to know exactly I can go and measure for you.
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Old 16 April 2008, 16:17   #24
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Originally Posted by jwalker View Post
Given that they need to go through the flange and that the pointed tip does very little then 1" seems about right.
In the centre section there is nothing. The hull has two full length (almost) longitudinals. They start at the transom where the support knees are and they are (should be ) parallel.
Yeh, I reckon. I held everything to the deck of my Destroyer using self tappers and silicon for a seal, 50gallon stainless tank, console, highbacked seats, hold-downs for ratchet straps and bracing for a 7ft high frame. Nothing came loose and the hull didn't leak.
As I said, I don't know your seat flange but if it's 6mm or so thick and properly moulded it will be strong and I'd not be using the washers.
Raised head screws are good because the countersink locates the screw into the flange and helps prevent any sideways movement. The slight domed head looks good and prevents the sharp edge that countersunk screws have if they stand a little proud.
I used a screw spacing of approx 70ish mm for my seats. If you need to know exactly I can go and measure for you.
So your saying you put screws 70mm apart roughly? no need so to put a screw in every hole in the flange on the sides of the seat?put one every 2nd or 3rd hole maybe depending on how far apart hole are.no need for washers so if screw fits ok into flange. ye its about 5-6mm thick..
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Old 19 April 2008, 06:00   #25
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This makes interesting reading...

http://www.maib.gov.uk/cms_resources/Abersoch%20RIB.pdf

Joe
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Old 19 April 2008, 07:13   #26
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serious stuff.

Have mine fitted correctly since yesterday. used all holes on flange for self tappers. 30 screws and sikaflex now holding it down so don't think it will be going anywhere
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