Filling up wrongly cut bow thruster holes

[samir elbaguer]

Hi all,
We had to cut an old bow thruster tunnel out and want to install a size smaller tunnel.
What would be the right way to fill the roughly 2 inches gap all around the new tunnel? The hull is solid fiberglass.

 

[Blueknarr]

One could always do a full 1-10 taper FG repair then cut a new hole.

But

Depending on the tube material and construction details there may be quicker easier acceptable solutions.

So
What's the tube made of? And picture
Do you know which FG cloths were used in the original construction?

 

[samir elbaguer]

One could always do a full 1-10 taper FG repair then cut a new hole.

But

Depending on the tube material and construction details there may be quicker easier acceptable solutions.

So
What's the tube made of? And picture
Do you know which FG cloths were used in the original construction?

The new tunnel is made out of fiberglass. They recommend using isophthalic resin to bond it to the hull but I would rather use epoxy if possible.
Sadly I don’t know what cloths were used.

 

[comfisherman]

Can you get to the backside of it?

I'd probably do a heavy taper of the inner portion, then use some waxed melamine to make an external form, then do a heavy layup tapering in the gap.

 

[fallguy]

That patch is done over the old hole. You simply apply the first piece of glass over the old hole and make it say 1” bigger all around. Allow it to cure and next day sand it a bit. Then make a putty and rough fill the first patch and make progressively larger patches until you are all the way out. There are a few tips to doing it.

You’ll need to cut out for the new hole after the first pass or at the end. You can use a sanding drum on a screwdriver after cutting an underbore say 1” od.

Use csm and tear, don’t cut the edges.

Calculate the needed layers before you start. If the csm is 0.030 per layer; you want to use say 6-8 layers; generally,

The last layer ought to be out past the new gelcoat by the tears so when you sand; you can get fair and below the gc all around.

 

[wet feet]

That will be an absolute pig of a job to do well.It is incredibly difficult to achieve a quality bond beneath a thruster tube at the best of times.It also will be a unique change in my experience as people never seem to downsize their thruster.I strongly advise seeking out the guidance notes from Sleipner,regarding the blending of the tube into the hull surface.Done correctly,it will reduce both noise and drag.The advice to use isopthalic resin is sound and it will be easier to add a compatible gelcoat and arrive at a good finish.

 

[samir elbaguer]

Can you get to the backside of it?

I'd probably do a heavy taper of the inner portion, then use some waxed melamine to make an external form, then do a heavy layup tapering in the gap.

It easier to get to it from the outside. Do you think I can use epoxy? Also, what kind of cloth? The lower half of the hole is about half an inch thick, the rest is about a quarter.

That will be an absolute pig of a job to do well.It is incredibly difficult to achieve a quality bond beneath a thruster tube at the best of times.It also will be a unique change in my experience as people never seem to downsize their thruster.I strongly advise seeking out the guidance notes from Sleipner,regarding the blending of the tube into the hull surface.Done correctly,it will reduce both noise and drag.The advice to use isopthalic resin is sound and it will be easier to add a compatible gelcoat and arrive at a good finish.

 

[samir elbaguer]

The reason for the downsizing is that the original installation was too close to the waterline and cavitating like crazy.

 

[comfisherman]

I used vinylester on my own install, with a couple different weight and weave orientations. My situation had miserable but doable access on the inside so was predominantly an interior layup.

 

[samir elbaguer]

Do you think it’s doable with epoxy? I’m more comfortable working with this material. Also, what cloth combinations would you recommend?

 

[comfisherman]

Can't comment on epoxy, I've only used it in hobby applications. The cloth combos I'd use would involve csm so wouldn't be very useful for epoxy.

 

[samir elbaguer]

I can use whatever. It’s just that I have more experience with epoxy.
The problem I’ve always had with polyester is the narrow time window.

 

[fallguy]

If you use epoxy; you cannot finish it with gelcoat.

But if this is in the antifouling; it doesn’t matter.

 

[C. Dog]

Hang in for a bit Samir, there are some forum members, expert with composite layups, who haven't commented yet. As we all know, it is a tricky job you are facing, and needs to be of excellent quality, or you are back to square one.

 

[ondarvr]

It's not difficult to downsize, even by 2 inches.

Position the new tube securely in place by using 3 wood wedges on each end. Put a thin layup between each wedge from the hull to the tube, when cured, pull the wedges out.

Start on either the inside or outside, your choice, put masking tape on the opposite side to put a thin layup against, it doesn't need to be strong, so one layer is fine. When that cures you now have the tube in the correct place and a surface to put the structural laminates on and recreate the hull thickness in what was the gap. Extend the laminate out onto the hull the normal amount, it will be plenty strong.