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Old 12-08-2009, 20:54   #1
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Mast Support Post

I have had some problems with Mast pumping, so I tuned the standing rigging before are trip around Vancouver Island. Pumping decreased but suspect I will have to change Mast post in side of boat(deck stepped mast) the inside post support is made of wood and I am thinking of replacing with 3 steel pipe .
I will re-bed the support at the foot . any advice appreciated. One thought if this post is made to measure without room for expansion or shortening it may be a problem to fit so I am hoping I can jack the crown of the deck up 1 higher than finish grade insert the steel post and let the deck settle back down. Is this possible or is there a better way ?
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Old 12-08-2009, 21:45   #2
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Is there any evidence that your compression post or under it is rotten? It should all be solid from the base of your mast to the top of your keel. Yes, you can replace it but I'd use stainless pipe rather than steel if you can. You can jack up the couch roof after slacking the rigging and squeeze the post in then retune your rigging.
regards,
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Old 12-08-2009, 23:34   #3
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If there is no evidence of deterioration of the post, that's not your problem. Have you checked under the sole to see what the support is like. Usually problems with the mast support are because of deterioration of the mast/post base in the bilge because of deterioration caused by water.

Sometimes water infiltration in the step on the deck is also a problem. The deck mast support is usually a plywood sandwich that is especially prone rot if water gets in on a regular basis. You'd be able to see the deck flexing if that was the case.

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Old 13-08-2009, 03:29   #4
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You may also be interested in our earlier discussion
Mast Pumping - Is This Normal?
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Old 13-08-2009, 04:46   #5
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I have had a similar problem that I solved by using for mast support under the cabin a 2 part steel pipe,that can be inserted in each other. the upper half is threaded on 10 cm length with 2 locking nuts. it can be inserted in the lower half, then the lower nut can be loosened thus lifting the upper pipe to the required height ( mast shrouds must be loosened) then the upper nut ( locking nut ) will have to be tightened against the lower one to avoid it coming loose.
hope this solves your problem.
Georges
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Old 13-08-2009, 07:54   #6
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Thanks all for your needed suggestions.
All I know for sure now is that the mast is pumping in wind at dock even after tuning. The top of the deck is not crowned but more depressed but not flexing under loads. The post is made of laminated strips of wood (1 inch long strips 8 foot) post is approx 4” X6 “ outside dimensions rectangle hole in middle for wires etc. The bottom of post is supported only on 3 sides with a 11/2 grove in the middle to allow water to run by. I am suspecting this may be the area of concern. When sitting at the table below and there is a 20 K wind I can feel a slight shifting of the post (very slight) and I suspect that the front part of the foot that is not supporting the post allows flexing forward. This is all speculation and I am planning this winter to put the boat on the hard take dimensions then remove the mast and rigging ( another interesting point is all my turnbuckles are almost bottomed out which points to mast lowering or all wires stretching) remove the post and ck for rot in the bilge area. I am all on my own no experts around to give advise so I have come to value this setting where experts from around the world can give clues as to what to expect or not. Thanks again everyone
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Old 13-08-2009, 17:37   #7
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Compression posts are built to support the mast from the bottom of the cabin top to the top of the cabin sole in most cases. I would suspect that the area of concern is from your cabin sole to your keel. That's where most boats have the problem. Can you reach and see that area? If you can't see it but can reach it just try to feel mushy or spongy wood or anything flexing.
Good luck in your search. In older boats that may get a lot of freshwater in the bilge (from a shower not draining properly) this is not an unusual problem.
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Old 13-08-2009, 18:50   #8
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This is not how my compression post was and but I will tell you how is is now.

In my bilge I have a ss shoe that is substantial and has tabs that generally form/slope to the shape of the bilge at that area (on top of my lead keel). It has a flat bottom with a ss pipe 3 1/2" ID welded to that flat bottom. The shoe sits in a bed of epoxy and fiberglass and I have tabbed in with fiberglass the ss tabs to the hull. The compression post has an outside diameter of 3 1/2" with a 3/8" +- thick plate welded onto the top end of the post. The deck has a 3 1/2" hole cut through it. The compression post slides through the hole from outside and then down into the shoe/sleeve. In the shoe/sleeve two 1/2 diameter ss pins slide through two 1/2" (one above the other) holes that are in both the shoe/sleeve and the compression post. These pins lock the compression post to the shoe/sleeve. I have put four 1/2" diameter threaded holes into the corners of the ss plate and matched my aluminum deck step with aligning holes. I then have 3 1/2" x 1/2" ss bolts that bolt the deck step to the ss plate (this is all above the deck). The 3 1/2" bolts then carry on down through 1/2 holes that I have put through my deck. Now when you are inside the boat you will see the bolts sticking through. Then because I have a flat deck (Corbin 39), I have taken two (1 on the starboard and 1 on port side of the compression post) 4" x 4" x 1/4" T6061 aluminum angles bolted to these protruding 1/2" ss bolts up tight to the ceiling. These angles run from my compression post (actually from about a foot further toward the bow) back to a bulkhead in my pilothouse and are supported there (about 11'). These four 1/2" ss bolts pull the angle up to the underside of the deck and then up to the underside of the ss plate that the deck step sits on. This is all sandwiched tight with sealant in between providing a very good seal and more support for my flat deck. It is also glued along the lenght.

My mast and rigging forces come down on my compression post while my deck gets additional support from the hanging angles.

My deck is in fine shape, I just know that "flat" is not very structural geometry and so added some help. It also provides an excellent chase to get from my mast back to my instruments in my pilothouse. Being 4" deep and 10" wide it will also provide for air distribution if I add air conditioning in the future.

I know the above is pretty wordy, I'm just trying to be clear.

Regards,
Extemp.
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Old 15-08-2009, 15:29   #9
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“ The deck has a 3 1/2" hole cut through it. The compression post slides through the hole from outside and then down into the shoe/sleeve. “ Very interesting concept Corbin has a great reputation and was one of my top choices before buying this Maple Leaf 42.Thanks Extemp.
The more I look into it the more I believe the problem is with the foot in the bilge area.
My foot is made from 4 pieces of wood that have been tapered and wedged into the bilge area trying to displace weight to keel and sides. If anyone has more details regarding the how to build the foot of deck step mast in the bulge area it would be appreciated possibly a web site etc.
SkipperJ
“I would suspect that the area of concern is from your cabin sole to your keel. That's where most boats have the problem. Can you reach and see that area? If you can't see it but can reach it just try to feel mushy or spongy wood or anything flexing.”
I will not be to the boat for another 2 weeks and then to bring up the Fraser river and on the hard once there I plan to remove the mast for inspection of the standing rigging. Once removed I will have the freedom to remove the post and inspect the foot properly at which time I may have to create a stronger foot support. I am not sure how to do this part Epoxy over existing wood , total epoxy as you can imagine noting is straight in this area just in the area where the hull curve begins to drop to form the keel
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Old 15-08-2009, 16:36   #10
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With a deck stepped mast, once the mast is lifted, the deck will spring back a bit and make space for any new post you want. But if the post is not rotten there is no reason to replace it. And a steel tube might be WEAKER than a wooden post - see any table comparison of mechanical properies of boat building materials.
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Old 15-08-2009, 17:37   #11
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Thanks barnakiel
Interesting I did not think the wood post was that strong.
It would be nice to find that the (only) place I will have to do any work is the foot .
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