Replacing Stern Bearing Housing and replacing with a FRP shaft tube

BillD

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Much has been written and pictures posted on this forum about this topic.
Samhop posted his conversion project. Larry, Travis and others have posted.

In a couple of weeks the my glassing in of a FRP shaft tube replacing the bronze stern housing will begin.

The new shaft will be 1.75" and the tube will be 3" OD.

The deadwood on the 25 T Jason has a rectangular end with no taper.
4" wide by 6" tall.

My plan is to maintain the distance on the boat now of the prop to the rudder.

Her's 2 or 3 pics of present and planned.

Seems to me the 3" round shaft tube sticking past the deadwood is a good improvement to water flow versus the bronze stern housing.

I'm thinking of cutting or grinding the edges "tapering" the flat rectangular edges of the deadwood around the exposed tube. I figure there's only 1/2" on either side and an 1.5" top and bottom of the tube to taper. Or leaving it "as is" with the tube sticking out is an improvement in water flow over the bronxe housing.

The shaft size in pic #2 is 1.25"

Stern Tube #5.jpg

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F/V First Team

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It's going to be easier to just cut the square out and go from there. A skill saw with a cheap carbide blade will do the majority of the work, a hacksaw blade in a sawzall will finish it off. Now you can grind to your hearts content on the inside and out and get a nice bond and support.
 

traditions

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I would fair out that rudder while your at it.Take some hull and deck and make it smooth,glass it over.That shaft being blunt is good for a knot.On my Holland,they used to be the same as you have there,when he started using tubes,he didn't change the mold,he just sticks the tube out to where the back of the box is and fairs it back to the stern post.No matter what you do you still have a 3 inch wide tube there,which is at the hub of the wheel and isn't that critical.The outside of the wheel does all the work.
 
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Badlatitude

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If i remember right Bill already plans to deal with the rudder. Might be in his tear down thread.
 

petrel

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I think we talked him into a new stainless rudder, right?
 

samhop

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tubing

jest cut the old " dead wood" out, tapper and from what i learned dont be afraid to bring the keel back.

for boats our speed say -30 Knots
the more the water terns before it reaches the prop the less efficient the prop will be. And from an engineer that used to work at P.W. now works at GE jet eng. div. "turbulence entering a fan is a huge problem"


the old way of thinking with max space keel to wheel was to let the water "heal" before it gets to the prop. that started in wood construction and is still present in a lot of keel trailing edge design. when you tube, you have the opportunity to improve the design efficiency. who much you improve it is up to you, jest a tube and taper where the bronze was would help. tapering, straitening and moving the keel back would help more.

FWIW sam



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captainlarry84

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Wow! some very fine glass work by to many. Bill are you saying that when you remove your bronze stern tube housing that the hole in the deadwood is square? Very odd that hole should be round. If it is round the boring is pretty simple. Just put two deep set hole saws on a very strong 1/2 drill. The smaller hole saw should be the size of the OD on the old tube. That will be a guide and do not cutting. The second hole saw will be the OD diameter of the new wet tube. That hole saw will do the work as the smaller one keeps you line up. Once the tube is slide in you can then adjust the tube a little to get shaft aliment close. Shim it in place then glass.
 

Toolate

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Boat currently has 1 3/4' shaft? Seems oversized no?

THis seems like a project that is up to you to decide how much work you want to do. I think you are going to see so much improvement in performance that you wont know the difference no matter what you do as any of it would be an improvement. I am the least experienced guy here but I would not grind on 1/2" of glass and intead would add to the back of the keel to the yellow line to ease the flow of water around the deadwood.

To really get to look like Larrys keel you are going to have to go Travis' route and I dont know if its worth it? Speaking in terms of performance. To have a gorgeous, homemade keel to brag about? I would volunteer you to itch for weeks.
 

BillD

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Wow! some very fine glass work by to many. Bill are you saying that when you remove your bronze stern tube housing that the hole in the deadwood is square? Very odd that hole should be round. If it is round the boring is pretty simple. Just put two deep set hole saws on a very strong 1/2 drill. The smaller hole saw should be the size of the OD on the old tube. That will be a guide and do not cutting. The second hole saw will be the OD diameter of the new wet tube. That hole saw will do the work as the smaller one keeps you line up. Once the tube is slide in you can then adjust the tube a little to get shaft aliment close. Shim it in place then glass.

Larry, I did not mean the hole behind the housing is square.
I'm assuming it's round. We'll see when I get it off.

I can make this conversion as difficult or as easy as I choose.

Enlarge the hole to accept the new tube and glass it in or cut the deadwood out and redo the deadwood and tube.

Time will tell.

Thanks for all the input.
 

captainlarry84

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Why cut the deadwood and destroy all of that original work. The double hole saw trick will get the job done. Once the hole is made to except the new wet tube you can then extend it as far as you like & if needed glass gussets top & bottom as shown in some of the early photos. To bad I am not closer I could bang that job out in a heart beat.
 

Brooksie

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the more the water turns before it reaches the prop the less efficient the prop will be. And from an engineer that used to work at P.W. now works at GE jet eng. div. "turbulence entering a fan is a huge problem"

the old way of thinking with max space keel to wheel was to let the water "heal" before it gets to the prop. that started in wood construction and is still present in a lot of keel trailing edge design. when you tube, you have the opportunity to improve the design efficiency. who much you improve it is up to you, jest a tube and taper where the bronze was would help. tapering, straitening and moving the keel back would help more.

I agree with this from experience... When I first had my boat, I added "fairing blocks" above and below the cutlass it bringing the blunt keel to a point. I thought I would try this instead if all the cutting, filling, grinding. This reduced the space between keel & wheel by 1/2 so I thought it may be a problem. It worked great, less rumble & 1/2k speed. It backs down better too I think.

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Toolate

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Great idea Brooksie. Short of reworking the whole keel this seems like it would reduce the turbulence by eliminating the place where the eddy/turbulence behind the deadwood can happen. Would think there might be a point where those fairing blocks you have could be too close to the prop though.
 

Brooksie

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Great idea Brooksie. Short of reworking the whole keel this seems like it would reduce the turbulence by eliminating the place where the eddy/turbulence behind the deadwood can happen. Would think there might be a point where those fairing blocks you have could be too close to the prop though.
I'm sure there is a point where they will be too close but what samhop was saying was look at a turbine, the stator and rotor pass very close for maximum efficiency so maybe the idea of all that space, like 15% of propeller diameter, is counter productive.
 
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