Mast step advice Hunter 490

[pinto]

Hello, I'm seeking advice on remedial work and a good solution for re-fitting my boat's mast foot.

The boat is a 16' Hunter 490. Aquired as a project, but would like to sail one day! Mast is a replacement Selden - quite a large section for the size of boat. Rig is mast head - large genoa small main era - came with a Plastimo furler.

There is a mahogany compression post which looks in good condition and is just proud of the cabin top by a few mm - which may be an issue - I'm not sure if the cabin top has sunk a bit. The cabin top is thick layup in this area 10mm at the front and 7mm at the back. The grp is solid and still in original gelcoat.

As can been seen there are numerious holes from former mast foot fastenings - all redundant and filled with silicone. Underneath there was a smeared lump of hard gunk - I assume to stop leaks - pulled away easily enough. The two cracks in the gel coat in the aft corners are not visable in the laminate from inside - I assume best to drill a small/shallow hole at the end of each and deal with when I get round to other gelcoat repairs? The Selden foot was fastened with two m5 countersunk bolts with penny washers underneath at the front and two screws into the end grain of the compression post at the back. Neadless to say the screws were loose and the foot rocked when lifted by hand.

Two issues: How best to address the holes and how best to re-fasten the foot.

Would it be best to use a large countersink bit to vee out the previous holes and fill with epoxy and 402 filler to make good the cabin top firstly? It seems a bit more structural given the forces on this area than just routine hole filling with thickened epoxy.

I'm assuming using longer wood screws into end grain isn't a good idea(?), so I'm wondering about fabricating a stainless bracket which acts like a saddle either side of the mast (cant go fore and aft because of the through sheaves for the keel lifting wire) and has a plate on top of the post which the mast is bolted to including through the deck (at least at the front). Obviously this would necessitate widening the gap in the cabin top either side of the post. Unfortunatly there isn't much flat surface behind the compression post for the foot to bolt through - If I used the same front holes, I would have to drill out the two shallow holes in the top of the compression post to accomodate the nuts for the two aft fastenings in the foot, which may set up a water-rot trap (best to seal the end grain with epoxy?).

Any thoughts or suggestions would be very greatly appreaciated.

 

[chris-s]

If it was my boat… I would …

1. Clean out all the existing holes with a countersink bit to be refilled with thickened epoxy.

2. Remove the compression post, fill the hole and repair the cracks with thickened epoxy and ideally add a few layers of heavy glass at least on the underside. Alternatively I might glass in a piece of 18mm ply as large as possible to spread the load from the compression post and give the mast foot something to screw in to.

3. Refit the compression post, using an acro-prop to raise the roof back to its height accepting that it might need to be trimmed to allow for step 2.

Good luck!

 

[William_H]

When sailing down ward loads are the main thing. Huge. Sideways location of the mast base is not critical except when raising the mast when the base can be pushed forward by the tackle. I note a 16ft is normally easy to raise mast but you said mast is heavy.
If the compression post seems robust enough just fit bigger wood screws at the back. Fill holes not used with epoxy. Perhaps a layer of GRP over the top of the post and area wood keep water out. ol'will

 

[pinto]

Thank you both for your replies.

Without moving the mast foot aft or the compression post forward I don't see how I can get away from using (bigger) screws. The only other solution I thought of was setting m5 threaded rod epoxied into the compression post and drilling out the mast foot to accept washers and nuts - allowing me to fasten from the top. The downside of this is that where the rod is glued into the post its quite near the corners and still in end grain, plus alignment would have to be spot on etc.

Chris - I like your idea of reducing the height of the compression post and using 18mm ply above it shaped to fit the cabin roof profile in that area. This would allow me to bolt through it at the front and give something much better to screw into at the back. As ol'will has said the forces are mainly compression, so I assume longer larger gauge screws through ply and then into the post end grain will be OK there.

The ply will also create a backing for filling all of the other holes!

- How is it best to glass in the 18mm ply? Should I encapsulate it using some cloth on the underside, or just bond it with thickened epoxy on top and press up using the post or a jack etc?

- Also is it worth considering g10 instead of ply for this application?

It seems having the post going through the cabin top is crazy - I'm unsure why this was done - it looked like there was some gelcoat on the top of it? The cabin will push up from inside to sit flush with the top of the post, so the fact they are seperate and bridged by the mast foot is not very strong! I think the original foot was a larger circular design which spanned over it.

In this area the lay up is about 8mm thick. I cant put an 8 to 1 chamfer into the sides of the hole left by the post because of the raised profile of the mast step area.

- Once the ply is in, how would I best fill this area to create a flat surface which is well bonded for the mast foot?

 

[wallacebob]

If you haven’t already, it’s worth joining HA Home Page . The 490 forum is reasonably active.

 

[William_H]

I had a problem with my 21fter in that it had an ali wedge on top of the cabin roof with support post under neath. The ali crumbled with corrosion so I laid up layers of chop strand mat with polyester resin to about 2cms at front to 1cm at back to get the base horizontal on a sloping cabin top. Worked well GP lasting for ever. To get the wedge shape I cut CSM in stages ie full length first then next one only 3/4 length next half length (from from to back)
In my case base was screwed down with 6mm bolts under the back heads attachment for boom vang etc.

 

[pete]

I would be tempted to make a disk out of tufnol or similar material perhaps 12 to 15mm thick, thicker if your rigging will stand it to cover the compression post and it's moulding, lowering the compression post if needed . Fix this down into the post away from the corners and through the deck forwards on a bed of your preferred sealer/adhesive then fit your mast foot onto this. Years ago I bought several sheets of Paxolin I think it was called (similar to tufnol) , 12mm thick and have used it for lots of things outside in the elements, it's workable with wood tools but quite hard and very rigid. This would spread the load from the mast foot to the compression post, seal the joint, cover up the mess and you could pull your deck up to it if you wanted. All assuming your rigging will stand the slightly extra height.

 

[pinto]

Thanks all for the replies and suggestions.

I have spoken to one owner who has an earlier boat with original spars. He is unsure if the compression post goes through the deck, but inside, within the cabin roof under the mast step area there is a substantial (factory original) for and aft moulding about 5 inches wide and around an inch or more thick. It appears the foot is screwed into this. My boat is significantly less well buit in this area! I'll post on the HA forum to enquire about other varients.

Pete- I think your suggestion has merit. Even is I am filling the rectangular hole left by the post with epoxy and cloth and using ply/ g10 underneath, the fact I can't put a propper camber around the repair means it will be weaker and this area would bridge the front and aft fasteneing of the foot - any flex being a serious stress riser, so creating a sandwich with a plate on top would significantly mitigate this - as you say if the rig will accomodate!