Propeller shaft plate bolts, any thoughts?

[Lucian]

Hello guys,

I have to apologise for the long thread but,
I hope that I can find some ideas or advice.
I am refurbishing an old 27 foot GRP boat, got the antifouling out, I repaired some blistering and now I got stuck at the prop shaft plate bolts. The problem is that all of the head of the bolts are rusted off (as in the picture) underneath the boat, inside the hull the bolts are covered in resin. I tried to get one out but witout any success.
I am appealing at the general wisdom and experience, maybe there is someone on here that was confronted with this type of problem. The way the bolts are stuck in the hull, I am conflicted, should I leve them as they are? My thoughts are that being a high vibration point will be a high stress point so I will have to change them.
Any idea how to get them out without mutch damage and how to reseal the new ones ?

Any thoughts are welcome, thanks for your help!

 

[rogerthebodger]

The pictures look like the inside of the boat with a threads showing.

I take it the underside of the boat is where the rusty heads are with GRP over the heads.

If this is the case I would grind off the GRP and heads of the bolts the if you can knock the bolts out from the inside. If not try knocking from the outside upwards.

 

[Lucian]

Sorry, I have attached the pic with the outside now.
I have tried knocking the bolt both ways pretty hard and hot nothing. When trying to knock the bolt out the boat was vibratin like I was knocking strait in to the structure.

 

[rogerthebodger]

I take it the fitting inside is metal If so could the bolts be threaded into the metal fitting

The key may be to cut the heads of the bolts under the boat and remove the inside fittings and bolts in one go by using a chisel between the inside of the hull and the metal sharft fitting

Can you remove the prod shaft completely what may give better access

 

[Tranona]

That is called a shaft log and is glassed into the hull. It is under little stress and as suggested they might be threaded into the plate, but more likely, even if you could get the nuts off the inside the bolts won't move because they are also glassed into the hull. perhaps grind away round the external area and glass a patch over the whole area say 10cm greater than the area of the plate. The internal glassing looks secure.

 

[sgodseafarer]

Hello guys,

I have to apologise for the long thread but,
I hope that I can find some ideas or advice.
I am refurbishing an old 27 foot GRP boat, got the antifouling out, I repaired some blistering and now I got stuck at the prop shaft plate bolts. The problem is that all of the head of the bolts are rusted off (as in the picture) underneath the boat, inside the hull the bolts are covered in resin. I tried to get one out but witout any success.
I am appealing at the general wisdom and experience, maybe there is someone on here that was confronted with this type of problem. The way the bolts are stuck in the hull, I am conflicted, should I leve them as they are? My thoughts are that being a high vibration point will be a high stress point so I will have to change them.
Any idea how to get them out without mutch damage and how to reseal the new ones ?

Any thoughts are welcome, thanks for your help!

Removing those bolts without causing too much damage can be tricky, but there are a few techniques you could try. Sometimes, penetrating oil and gentle tapping with a hammer can help loosen them up. If that doesn't work, you might consider applying heat with a propane torch – just be cautious not to damage the surrounding area. As for resealing the new bolts, using marine-grade sealant should do the trick.

 

[neil_s]

Brace the outside of the hull to the ground with a steel tube. This will stop the hull vibrating and allow you to drive the bolts out from inside.

 

[Lucian]

Thanks, I tried that, but it still nothing. I managed to remove the nut from inside the boat, and using a piece of wood and a hammer I started tapping harder and harder until the wood gave in. It feels like part of the hull. I do not want to force it to much, don't want to damage it.

 

[Lucian]

That is called a shaft log and is glassed into the hull. It is under little stress and as suggested they might be threaded into the plate, but more likely, even if you could get the nuts off the inside the bolts won't move because they are also glassed into the hull. perhaps grind away round the external area and glass a patch over the whole area say 10cm greater than the area of the plate. The internal glassing looks secure.

It certainly felt like the bolts are glassed into the hull. I was thinking that patching over is one of the solutions but I don't know how thick the hull is in that place so I don't know how is it going to be on the long run.

 

[Refueler]

1. You cannot apply heat as that can damage the GRP around it.
2. You cannot hit too hard as that can damage the GRP around it. Plus you risk expanding the end of bolt and making it harder to extract.

The old way of removing embedded studs / bolts - was to use a 'tube drill' .... basically its internal diameter is similar to the bolt / stud diameter ... the bolt then provides the guide to keep the tube drill cutting away round the bolt.
But I haven't seen such for many years ... likely now - you'd have to get one made.
But before you rush out for it ... a) GRP is actually a very hard material and destroys hole cutters when fitting logs etc. b) what is sandwiched inside that GRP ... if its a metal plate - then how to do it then ?

Are you sure you really need to replace ? New nuts of course but the bolts ?

 

[VicS]

Are you sure you really need to replace ? New nuts of course but the bolts ?

It is the heads of the bolts on the outside which are corroded . ( Re-read post #1)
The nuts are OK

 

[barryhall]

It certainly felt like the bolts are glassed into the hull. I was thinking that patching over is one of the solutions but I don't know how thick the hull is in that place so I don't know how is it going to be on the long run.

What about leaving the existing nuts and bolts in place and drilling additional holes through the hull and plate and then installing new nuts and bolts.

 

[Refueler]

It is the heads of the bolts on the outside which are corroded . ( Re-read post #1)
The nuts are OK

I saw that ... but TBH - the other posts on it seem to wander a bit - so thought .... can it be left ?

 

[ean_p]

I te d to think that the bolts have no function now and that they were used to fit and secure the tube while it was glassed into the hull. Now glassed and secure the positioning bolts are redundant. Grind off any external rust and glass over. Then monitor and forget.

 

[Lucian]

What about leaving the existing nuts and bolts in place and drilling additional holes through the hull and plate and then installing new nuts and bolts.

I think this is the best solution yet. This way I can prepare the outer hull and at the end just bolt four bolts (for good measure).

 

[Tranona]

I think this is the best solution yet. This way I can prepare the outer hull and at the end just bolt four bolts (for good measure).

That really is overkill. That style of stern tube was designed for bolting into wooden hulls, hence the 4 substantial bolts and is rarely seen these days. You don't say what your boat is, but guess it was made in the early days of GRP building and before it came the norm to just glass in tubes. Pretty sure the bolts don't do anything and were just used to locate the tube before glassing over. There is little strain on the tube - it is just there to attach the inner seal to. The shaft is supported by the engine at one end and what looks like an A bracket at the other.