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devemaster 06-04-2010 10:05 AM

Islander 30 MKII compression post substructure
I'm considering the purchase of a 1972 Islander 30 MKII. One of my main concerns is the condition/construction of the framework that carries the load of the compression post/main bulkhead to the hull.

Does anyone have hands on knowledge of this structure? Prefer to hear from someone who originally built the boat or has done repair work to this area.


devemaster 06-11-2010 07:29 AM

Hey Self-

Since posting we have both done a cursory examination of the substructure using a fiber optic scope. Looks like the area between the cabin sole pan and the hull is reinforced with a combination of chopped and woven 'glass although it is certainly not overbuilt. The compression post on this particular boat has rotated out of position about 3/4 of an inch and about 30 degrees axially.

Seems like the thing to do is to add some more reinforcement paying particular attention to any gaps between structural elements and resetting the compression post and reattaching maybe with 5200 or some other strong but relatively low modulus method.

Care should be taken to taper and reinforcement to avoid creating any stress risers.

Good luck and let me know how it turns out.

yours truly,


tonykeel 04-14-2011 01:09 PM

Pictures compression post base
I am considering purchasing an Islander 30 MkII as well. I have pictures of part of the substructure under the cabin sole under the compression post. It is not pretty. Would you like me to send them to you? This boat has about 3/8" compression of the cabin sole and substructure, and there is a plywood shim installed. Were you able to solve your problem and how did you accomplish it. I would like to determine whether this is worth fixing and if I should continue with the purchase of the boat.

tonykeel 05-06-2011 10:57 PM

cabin sole / compression post / construction
I decided to buy the boat and fix the 3/8th" of sag under the compression post. The construction was as follows. The bulkhead plywood fits into a slot which runs down the length of the compression post. Screws hold it in place. A 3" lagbolt through the mast collar, cabin top and aluminium plate is screwed into the top of the compression post. The base of the compression post rests on top of the fibreglass cabin sole. The fibreglass rests on a 5/8" marine plywood which is used to construct the raised cabin sole in the head. In order to transfer the compression load to the hull there is a fir wood block underneath the marine plywood. The bottom of the wooden block is taper into a a rough V shape and it rests in the V shape of the hull. The sides of the block are covered in a thin sheet of fibreglass. The bottom of the block is covered with some sort of hard bedding compound.

Problems with the construction which I think contributed to the 3/8" sag (i) the marine plywood compressed a bit (ii)there was a 3/8" void between the fibreglass and the plywood comprising a 1/2" channel, which made the starboard side of the base under the compression post a bit unstable (iii) the hard bedding compound had become brittle and some of it had chipped off.

Solution: In order to expose the construction it was necessary to cut out a rectangle in the fibreglass and then chisel and cut out the marine plywood and finally the wooden block. The V in the hull was made flat by adding fibreglass to create a flat base. A teak block will be installed to support the compression post and this will be finished in fibreglass.

harbin2 09-06-2011 07:45 AM

I recently replaced my standing rigging and upon tensioning, I realized I am having the same problem as you with my compression post and base. I'd appreciate any photos or additional information you have on the work you have done since I'm now considering the same. I have a Bahama 30 which, I believe has a larger compression post but I don't think Islander solved the problem buy just beefing up the post.
Thanks, Harbin2

GNI 11-26-2011 09:31 AM

Islander 30 compression post
we have the same issue on our 1976 Islander 30. We can not get the rig to proper tension. Could you please share your pictures with me also? I'm a new member so I'm not sure how this works.

thank you,


tonykeel 11-28-2011 02:44 AM

Sorry I did not get back to you. I was away for a couple months and then back to work! I will dig up the photos for you. It was not nearly as bad as it seems when you can't see whats under the sole. But once you cut the sole open it is not big deal. You just take off the mast, remove the compression post, cut out the sole, and you can see a block of wood with a v in the bottom that is kind of glued into the hull with a bedding compound. This bedding compound shifts over time and he sole bends down onto the block of wood as it settles. If I had known that this is what was under there I would have left the shim on top of the sole and just kept an eye on it. But I could not leave well enough alone and needed to did down to the hull.

I also split the compression post when I was reinstalling it and had to mill a new one from a beautiful piece of teak. I enjoy looking at it now and do not regret digging the whole thing apart and rebuilding it.

I also jacked up the cabin top about a half inch, to get rid of a pool of water that was hanging around the cabin top by the mast step. Also drilled the weep holes a little larger in the cabin step on top of the deck.

Retuning the rigging was no problem, there was lots of info on the net with different theories on how to do that.

What sort of difficulty are you encountering in tuning your rigging?

tonykeel 11-28-2011 03:18 AM


GNI 11-28-2011 08:42 AM

Thanks for the reply!

Our problem sounds very similar. We noticed the rig not holding tune and the puddle around the deck step. I'd really like to see what it is supposed to look like.

tonykeel 12-03-2011 06:33 PM

These pictures were taken by the surveyor and I marked them up to ask him questions in some cases, or to clarify what I was looking at for myself. The pictures are closeups and can be quite deceiving to look at. If you are patient with photobucket, and view them from in there, you will see comments under the pictures which explain what you are looking at. The first link will show you the pictures from the photobucket website where you will see the comments. I think the rest of the links will just show you the pictures.

c-postbottom52.jpg picture by ajaphotobucket - Photobucket

New to photobucket. Try this link for a view aft underneath compression post. I have some video and additional pics I will post.

Here is a video of the block half way through being chiselled out.

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