Slipper 17. Removal of Deck mounted mast support

[Jimc91]

Suggestions for removal of wood support for deck mounted mast on Hake Slipper 17 as the laminated wood board, 2x4 size, is soft on one side.

My questions to members is to confirm if the factory fastened the board end thru the top deck which probably means dropping the mast to gain access to fasteners?

 

[twistedskipper]

I think if you’re removing the mast compression post, you probably want to drop the mast first anyway?

 

[Jimc91]

Dropping the mast is probably the best idea, but this seems to be a very lightly loaded deck design. Since my initial posting, I have found that this compression post supporting the deck mounted mast is mostly glued in a formed pocket in cabin bulkhead at bottom with one small screw and lots of adhesive/sealant. What fastener that may have been used into top of board is yet to be discovered. This compression post only bears on the interior cabin bulkhead and the bulkhead does not bear directly on the keel in the center line of vessel. This cabin partition only bears on the hull at sides and farther back at entrance to companion way and onto the transom.

When the weather is better I may temporarily support the deck with two posts and then cut and replace the post with a piece of zebrawood which is harder than teak or white oak. It will be interesting to see how if there is a screw into top of post from the upper deck. All mast bracket bolts are visually accounted for at this time so it will be interesting to see if Hake Yachts only used an adhesive as this is the original post per the previous owner I spoke with. The bolts for the mast support bracket are most likely the source for the water damage to the post and I will take measures to prevent water entry from the mast bracket screws.

I had concerns this was a cored FRP construction and may have suffered some rot in the core, but it appears it is solid fiberglass and and ranges in thickness from 1/4' to 3/8+" at the radius corners. All glass is in very good condition without cracks.

 

[jssailem]

As mentioned in your first post, the Compression post is there to transfer the compression forces of the mast to the keel of the boat. This transfer is what allows sailboats to sail forward. You want the compression to be in column with the mast.

Unsure how any previous owners may had arranged the mast and the bolts. If the compression post and mast are not in column then you will have issues with your boat.

 

[Jimc91]

As mentioned in your first post, the Compression post is there to transfer the compression forces of the mast to the keel of the boat. This transfer is what allows sailboats to sail forward. You want the compression to be in column with the mast.

Unsure how any previous owners may had arranged the mast and the bolts. If the compression post and mast are not in column then you will have issues with your boat.

 

[Jimc91]

I am assuming by “in column” you refer to the post is directly under the mast. If you review the photos the compression post is a few inches slightly aft of the mast and none of the four mast bracket bolts penetrate the post. Having viewed many of these vessels online this is the common setup and post set on an angle. I did view a Seward boat that had its post vertical.

 

[jssailem]

It is the physics of a sail boat.

In simple terms, your sails fill with air. This cause the mast to want to lean with the wind. But your mast has shrouds that stop the lean. That force has to go someplace. The shrouds pull up on the hull, which resists the force. In doing this the shrouds pull down on the mast compressing it down against the deck. Here is where your compression post gets into the picture. The deck is forced down and the compression post carries this force down to the keel of the boat.

Your boat now has only two options pull itself apart of squirt forward. The squirt forward is the easiest so that is what it does until it pulls itself apart.

Oh how I love the magic.

 

[Jimc91]

"The shrouds pull up on the hull, which resists the force. In doing this the shrouds pull down on the mast compressing it down against the deck. Here is where your compression post gets into the picture. The deck is forced down and the compression post carries this force down to the keel of the boat.

Your boat now has only two options pull itself apart of squirt forward. The squirt forward is the easiest so that is what it does until it pulls itself apart.

Oh how I love the magic."
[/QUOTE]

Thank you for the ship physics review. My posting and description of the slipper 17 design is precisely the point of my observation in that the deck mounted compression post does not bear on the fixed keel, please reread my post. The compression post is positioned under the deck mounted mast and "bears" on a interior cabin bulkhead which does not contact the keel but contacts the hull at the port and starboard sides, so it would appear the deck sends loads to the hull and the keel is strictly just ballast . This was the reason for my question on the proper procedure to replace the damaged compression post and how to support the deck. As an important part of the design physics and bearing loads of this vessel it seemed odd that this compression post had few or any fasteners thru the deck into the compression post may only be glued in position.

UPDATE:
Yesterday I was fortunate to speak to Nick Hake and he said the compression post "could" be replaced without dropping the mast. simply loosen the lines and cut and remove. There are no thru deck fasteners for the compression post and it was glued/sealed in position and he suggested using 3M 5200 adhesive.

 

[Jimc91]

Update on Slipper 17 mast support post and how it is fastened to deck.

Over the past 40 years water has worked past the caulking on the top side screw which is located directly below the mast
support bracket topside. I have inspected the deteriorated wood support post which is set at an angle in a molded in pocket in the fiberglass bulkhead floor and I can see at least one possibly two thru deck screws that penetrate the top of the post.

I will soon replace the rotted wood post with white oak post but I am considering mounting it in a true vertical position rather than on an angle to port side. I have inspected the surrounding bulkhead but do not see any special reinforcements or structures and even the fiberglass is a consistent thickness, so it appears that the bulkhead carries common loads/stresses across the bulkhead port to starboard.

The designer's only comment was he remembered the post might have been placed on an angle due to possible future location of a
"head" in this area. I have not seen this in any other Slipper 17s.

I will use 3m 5200 to seal/glue the new post in position to cabin roof and bulkhead and insert a screw from bottom side of the
bulkhead to pin the new post in position at base.