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Questions on converting an old boat to a strut system.

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Questions on converting an old boat to a strut system.

Old 11-22-2006, 11:56 PM
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Sean Bowf
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Default Questions on converting an old boat to a strut system.

I have an old Dumas Lil Rascal that I pulled out of moth balls. I built this thing 20 or 25 years ago. The stuffing box is hard mounted in a wooden strut that runs along the bottom of the boat, from the point the stuffing boxes comes below the boat to the back of the boat.

As a kid, I split this strut and put a wood shim in it to put the prop lower into the water to keep the prop from cavitating. I know now that this is not how a rigger is supposed to run.

Anyhow, I am trying to figure out the new strut systems, to see if I can adapt this old boat.

Right now the boat has a 1/8th inch flex shaft that goes through a 3/16th inch brass tube. There is a rigid piece of metal at the end of the flex shaft that stays in the stuffing box. This hard piece goes down to a 1/8th inch threaded shaft for props. I am currently using a 3/16th inch prop that has a shim in it, so it will fit on the shaft.

If I can find a strut that will work on this boat, how does the stuffing box connect to the strut (or does it?)?

Below is a pic of the back of the boat. Any suggestions on upgrading this?? Or should I just be looking at building a new tub??

TIA for your input,
Sean
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Old 11-23-2006, 02:22 AM
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Sean Bowf
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Default RE: Questions on converting an old boat to a strut system.

Here is an example, if I picked up [link=http://www.seaducerboats.com/images/316hydrostrut.JPG]this strut[/link], what else would I need to do to adapt my old setup to use this strut??

I know I am removing the wooden strut that is on the boat now.

Then the current stuffing box, do I cut it off just short of the strut? Or does it run into the strut?

I get a teflon liner for the old stuffing box. How is it held in place? How far does the liner run? Does it stop at the end of the stuffing tube, or does it run into the strut?

New flex shaft...old one was 1/8th...the new flex shaft will have the stub shaft in the strut as opposed to the old setup where it is in the stuffing tube right? Does anything hold it in the strut? The old shaft just had a pin that ran through it to mount the prop on. I take it I will be going over to a drive dog. Does anything go between the drive dog and the back of the strut?

Sean
Old 11-23-2006, 02:32 AM
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Default RE: Questions on converting an old boat to a strut system.

If you are staying with that brass the teflon and strut must match along with flex cable. The teflon is a snug fit into brass. The teflon runs the length of the brass. It runs into the strut snug fit.
Old 11-23-2006, 08:42 AM
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Default RE: Questions on converting an old boat to a strut system.

ORIGINAL: Sean Bowf

Here is an example, if I picked up [link=http://www.seaducerboats.com/images/316hydrostrut.JPG]this strut[/link], what else would I need to do to adapt my old setup to use this strut??

I know I am removing the wooden strut that is on the boat now.

Then the current stuffing box, do I cut it off just short of the strut? Or does it run into the strut?
It depends on the strut you choose. Some struts are designed to allow the stuffing tube to run into them.
I get a teflon liner for the old stuffing box. How is it held in place? How far does the liner run? Does it stop at the end of the stuffing tube, or does it run into the strut?
There are two choices, teflon liner or two pieces of brass tubing. When you use two pieces of brass tubing, the inner one can go into the strut. The outer one can stop just past where it exits from the boat hull.
New flex shaft...old one was 1/8th...the new flex shaft will have the stub shaft in the strut as opposed to the old setup where it is in the stuffing tube right? Does anything hold it in the strut? The old shaft just had a pin that ran through it to mount the prop on. I take it I will be going over to a drive dog. Does anything go between the drive dog and the back of the strut?
Unless you use a square drive setup, there will be nothing between the drive dog and the strut. The shaft will be held in by a collet connected to the engine. With this setup you actually need to leave some space between the drive dog and the strut because the flex shaft gets slightly shorter when the boat is running.
Old 11-23-2006, 09:07 AM
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Default RE: Questions on converting an old boat to a strut system.

What are the pros and cons of a square drive shaft? Would it allow me to dynamically move the 10 ounce engine 1/2-3/4" to modify the CG?

What about flex shafts versus straight shafts? Couldn't you use a straight 1/8" shaft instead of a flex 3/16" for a hot 21?

Has anyone mounted the engine farther forward and run a straight shaft from engine through the stuffing box and then have a small flex shaft just prior to the small straight prop shaft through the strut? It just seems that a straight shaft with bearings would have less friction and power loss than a flex shaft bending and rubbing on shaft log and strut. Has anyone tested this?

On this Thanksgiving, I am so thankful for all the experience that everyone is willing to share to help a technical newcomer!
Old 11-23-2006, 09:21 AM
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Default RE: Questions on converting an old boat to a strut system.

ORIGINAL: 007clint

What are the pros and cons of a square drive shaft? Would it allow me to dynamically move the 10 ounce engine 1/2-3/4" to modify the CG?
Uh oh, not this discussion again! I no longer run square drive. The pros at the time included not placing any thrust on the engine bearings, and very low risk of losing the prop if the shaft breaks. This was because there is additional hardware at the back end that locked the stub shaft into the strut. The cons of the square drive is that it was less convenient to remove and grease the shaft, and there was more hardware on the back to deal with. The engine position was no different than you would have for the other type of flex shaft, the collets are about the same size.
What about flex shafts versus straight shafts? Couldn't you use a straight 1/8" shaft instead of a flex 3/16" for a hot 21?
Sure, you could use a solid shaft. However, you're going to need to do something to change the angle so the prop thrust is parallel to the boat hull. This would usually be some type of universal joint. By the time you've done this, you may find that the flex shaft is simpler.
Has anyone mounted the engine farther forward and run a straight shaft from engine through the stuffing box and then have a small flex shaft just prior to the small straight prop shaft through the strut? It just seems that a straight shaft with bearings would have less friction and power loss than a flex shaft bending and rubbing on shaft log and strut. Has anyone tested this?
Lots of testing has been done in the past, I don't know all the details. What I do know is that in North America most use a flex shaft setup and they're setting lots of records. If you've got an idea that you think might work better, go ahead and give it a try, you might revolutionize the way shafts are done.
On this Thanksgiving, I am so thankful for all the experience that everyone is willing to share to help a technical newcomer!
Happy Thanksgiving!

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