Rudder Installation Questions - 1979 Classic Ski Boat

[ScrewPull]

I have been doing some light restoration work on my 1979 MasterCraft Stars & Stripes. While waiting for a swim deck bracket to be made, I decided to inspect the fiber-glass covered wooden mounting plate that's beneath the Rudder Log Plate. The glass matting looked delaminated at the forward section of the plate, so I knew I was in for a fun little project.

As I suspected, the wood beneath the glass was pretty well compromised. Glad I decided to look into it, although I've created a rather large bag of questions that need answering. I've tried getting answers at my MC forum, but haven't gotten anything. This forum seems to be far more comprehensive, so I am hoping I can get the answers I need here.

The questions I have are as follows:

1. In replacing the square, wooden plate, what is the best kind of wood to use? I am sure some kind of marine grade ply would suffice.

2. In relation to question number two, what is the best resin to use? I have some West Marine Boater's Polyester Resin and some West Epoxy Resin (105, with 206 Hardener and some 404 High Density Adhesive Filler). I also have glass matting.

3. Also in relation to question 2, can I use another substrate for the plate? I have some thick Star Board that would appear tobe a great alternative, but I want to make sure it will adhere to the resin and fiberglass. That said, would my choice of resin be different if using star board rather than wood?

4. I need to know what the proper approach is to getting the rudder alignment correct. I have searched high and low and have yet to find anything on proper rudder installation. Can anyone help with this?

The red arrows below point to the forward two corners of the glassed-over wooden plate.



Nice stuff!



Cleaned up the area a bit.



Any help would be greatly appreciated!! Thanks!

 

[chconger]

1) White Oak would get my vote. About the best for rot resistance. Teak is great too. Careful not to use red oak - just about the opposite of white, as far as rot resistance.
2) Epoxy is stronger & bonds better than poly. It's more expensive, but your not using much here.

Cheers

 

[ScrewPull]

Thanks, CH!

On the White Oak, are you meaning a White Oak Ply?

 

[alldodge]

Agree, white oak is best with solid woods, but I would use Marine grade or BC exterior grade plywood, Reason for ply wood is to provide better structural support. Defiantly use epoxy resin over any other, bonds better and is water proof if you get penetration through the glass.

As for the centering the shaft, I would guess the wood was glassed in and the hole was drilled in the center later. This was done after alignment was done to make sure the rudder was in the center of the prop shaft. This in my opinion is why it was to one side of the block of wood.

 

[ScrewPull]

Agree, white oak is best with solid woods, but I would use Marine grade or BC exterior grade plywood, Reason for ply wood is to provide better structural support. Defiantly use epoxy resin over any other, bonds better and is water proof if you get penetration through the glass.

As for the centering the shaft, I would guess the wood was glassed in and the hole was drilled in the center later. This was done after alignment was done to make sure the rudder was in the center of the prop shaft. This in my opinion is why it was to one side of the block of wood.

The off center Rudder Port in relation to the wood backing is a factory design. I am guessing it has to do with more structural torqueing to the port side. Guessing here, though. But every S&S I've seen looks just like in my photo.

I thin my question in reference to alignment was more in relation to the rudder shaft being perpendicular to the overall plane of the boat from side to side and what angle would be required, fore/aft? So, in essence, I want to make sure the plane of the new wood backing plate is proper side to side and front to back.

Centering it is certainly critical, but I'm thinking my holes are pretty well where they need to be. Will double check in relation to the shaft.

I agree on the plywood. Can one get marine grade ply at Home Depot? Will check their website.

 

[ScrewPull]

By the way, thanks for your input, All Dodge!

 

[ScrewPull]

Well, now that I look at it, it appears that the shaft stuffing box is actually a little off center. Appears to be about a 1/4" to the starboard side.

Does anyone know if this is by design? I know zero about rudders, as y'all can tell. But I've actually seen boats with it slightly offset.

I have used the boat since 2010 and never noticed any problems.

In the case that it needs centering, I'll need to fill the holes and re-drill. What a pain. The center hole through which the log goes is wider than the actual log itself, so I may not have to do much there, but the mounting holes will definitely need filling/re-drilling.

Any suggestions on the best filler?

 

[alldodge]

Tried hard to get marine grade from HD, Lowes and others for my rebuild of my boat, no good. Settled on BC exterior from HD and had great results, used two 3/4 and one 1/2 sheets to get it all done.

You might be right with the forces to one side over the other due to prop wash load

So far as perpendicularity, I would mark a line from one side to the other which would be level. To get the exact level I would use the same location on both sides and be the farthest point I could use and be certain they where the same location with reference to the hull. Once marked, adjust the hull with jacks to put those points at the level. Then use a plumb bob and string to find the perpendicular plane.

Bore the hole through the plywood on a drill press slightly larger then needed. Bore the same hole through another double thickness in a separate piece of wood. Mount the rudder bracket to the wood (temporally), now adjust the wood against the hull to find the location. Mark and remove bracket.

Now glass the wood into place and on the inside of the bore. Once cure, use the double thickness to re-bored the hole through the original wood which was epoxied

 

[Ned L]

I would personally use mahogany for the block. Real mahogany is also quite rot resistant. A disadvantage of oak is that oak is not very dimensionally stable ( it changes dimension a lot with wet & dry cycling, not what you want when bound by glass.). Teak is soft.
As said, epoxy resin is better than polyester resin (stronger, truly water proof, bonds better old & dirty original glass.)
Often times rudders are installed slightly off center to allow the prop shaft to be pulled without dropping the rudder (or pulling the engine).

 

[chconger]

Janka Hardness & rot resistance, According to the wood database:



White Oak : 1350 lb[SUB]f [/SUB]Rated as very durable; frequently used in boatbuilding and tight cooperage applications.


[SUB]Honduran Mahogany : 900 Lbf [/SUB]Varies from moderately durable to very durable depending on density and growing conditions of the tree


[SUB]African Mahogany: 1070 Lbf [/SUB]Rated as moderately durable; moderate to poor insect/borer resistance.


[SUB]Teak: 1070 Lbf [/SUB]Teak has been considered by many to be the gold standard for decay resistance, and its heartwood is rated as very durable

 

[BillP]

Couple of comments. Why put something that can rot? I would be tempted to lay the whole void up in frp and be done with it. You would have to watch heat build up if doing it all at once so that's a consideration. Use laminating resin if you go that route and polyestger will work fine. Epoxy is overkill and un-necessary expense in my opinion. Another thought, use pressure treated wood. As far as worrying about wood adhesion of the glass, the shaft log will mechanically clamp whatever media you put there...sheer load on those bolts is not going to move a clamped piece. Traditional wood ski boats have been doing it that way for decades without issues. A pt ply block glassed over and clamped down will work and last as long as the boat too. Had the mfg done it originally that way you wouldn't be dealing with it now.. As far as the offset, it may be there for tor propwash offset but I would think this could be verified though a few current ski boat companies for fact vs opinion...

 

[ScrewPull]

Great information! Thanks to you all!

I think whatever the wood will be is going to be a plywood of one nature or another for structural integrity. That's what came out of it.

I would like to know what anyone thinks about using Star Board. I have a piece already cut to the dimensions of the plate, but am unsure if it will adhere properly to the Resin.

As far as the rudder being a little off center, I am beginning to believe that it was designed that way, so I am not too concerned. Will make sure before I replace/re-glass it.

Thanks again! This is a great forum!!

 

[alldodge]

IMO I would not use star board, because while it is good building material it does not have the same load carrying abilities of plywood. Thought about using star board in my hull rebuild but found that you cannot install screws into it like plywood. Star board must be thru bolted with plates on the back side to hold

 

[ScrewPull]

Plywood it is, then. Thanks Dodge!!

Quick question on curing time... How long do I wait before re-installing the rudder and actually using the boat? Just want to make sure I don't stress it prematurely. I've done a little bit of glassing, but time has never really been an issue before putting to use.

 

[alldodge]

The manufacture of the resin you buy will have all the info as far as mixing, temp and curing time. They make 1:1 to 4:1 mix ratio and the higher the number the quicker it sets. Pay special attention to cure temps, the ones I found use 70 to 90 degrees as optimum. Anything below or above either need to wait or note procedures for using. Most epoxy resins cure and ready for use in 24 hours

 

[ScrewPull]

Ok, that's what I figured. Everything I've used in the past - both epoxy and poly - have cured relatively quickly. The heat here in Houston is pretty awful, so at time, I've noticed it to take a bit longer on some things to be dry to the touch.

Thanks again, Dodge!