Extension shaft for a 4HP Merc

[Lancerdad34]

I just got a 4 hp merc for a trolling motor but it is not low enough in the water. I have not seen anywhere that I can get this. does anyone know where I can get one?

Thanks,

Brian in MI

 

[Chinewalker]

Year? Serial? Later model 4s had a 5-inch extension you could add in and swap out driveshaft, add water tube extension, etc. Earlier 4s had a unique long exhaust housing that would need to be swapped, along with the driveshaft, shift rod and water tube. Best bet would likely be to sell the short and buy a long shaft motor...

 

[Lancerdad34]

Thank for the reply! That is what I am going to do. Get by with it the rest of this season and sell it next spring and find a long shaft.

 

[JimS123]

For a kicker you don't need to worry about the position of the anti-vent plate. As long as the prop is below the bottom, you are good to go since you won't be planing anyway. If you have a long swim platform type transom, and the motor is mounted far aft, a higher prop might be OK too. The point is, try the SS first and see how it goes. You might not need a LS after all.

Last year I swapped out a LS for a SS and found I get better top speed due to less drag in the water.

 

[Lancerdad34]

Thanks for the reply. I have one of those drop down brackets mounted on the stern. My prop is in the water but up above the bottom of the boat. It pushes me along OK for walleye but if its rough it pops up out of the water sometimes, plus it does not give any control of the boat. Thus I am going to go with a longer shaft motor for next season.

 

[JimS123]

Most drop down brackets are adjustable. Maybe try lowering the bracket a few holes.

If all you have is 4hp, the boat (and transom height) can't be that big.

Just trying to help you save money...

 

[Sea Rider]

A under powered OB used as a kicker will push much better if correctly height seated and propped right to run at max wot rpm range factory stated as usually loaded.

Happy Boating

 

[JimS123]

A under powered OB used as a kicker will push much better if correctly height seated and propped right to run at max wot rpm range factory stated as usually loaded.

Happy Boating

That's true but not always possible.

The "std" prop for a 4 is probably designed for a very little boat. What is needed is a very low pitch prop, or sometimes called a "sailboat prop".

Unfortunately, there is only one choice made for a Merc 4. Since those props are usually plastic they can't readily be re-pitched.

 

[Lancerdad34]

Thanks for all the help on this issue. I have been getting by with the 4hp but as I said before when it is rough it is hard keeping the prop in the water. I have a Brother-in-law that has a 9.9 long shaft Honda 4 cycle that I will look at and most likely buy for next season. The nice thing about that motor is I can run a fuel line off the main tank.

 

[JimS123]

Thanks for all the help on this issue. I have been getting by with the 4hp but as I said before when it is rough it is hard keeping the prop in the water. I have a Brother-in-law that has a 9.9 long shaft Honda 4 cycle that I will look at and most likely buy for next season. The nice thing about that motor is I can run a fuel line off the main tank.

That's a real heavy motor. Better make sure your bracket can handle that much weight. These days they make heavier brackets made specifically for 4-strokes.

 

[TOHATSU GURU]

If that 4 was made in the last 25 years there are a variety of propeller options available for it. Including one designed to push a load.

 

[JimS123]

If that 4 was made in the last 25 years there are a variety of propeller options available for it. Including one designed to push a load.

OK, I have a 2017 Mercury 3.5 HP 4-stroke. They only have 1 prop listed. Same for Michigan. I DID find a Tohatsu prop of slightly different pitch, and it was better, but not optimum.

So, can you provide a link to a prop to push a load with my motor?

 

[TOHATSU GURU]

The 3.5 is a different engine than the 4 and requires different propellers. Any Tohatsu dealer can sell you a 4.5 pitch propeller. In theory that should provide enough RPM to push a load of 1700 lbs. I can't post a link as that would violate iboat's policy.

 

[JimS123]

The 3.5 is a different engine than the 4 and requires different propellers. Any Tohatsu dealer can sell you a 4.5 pitch propeller. In theory that should provide enough RPM to push a load of 1700 lbs. I can't post a link as that would violate iboat's policy.

Thanks for the info. I swear I googled this last year and only found 6 and 7 pitch props. And that WAS Tohatsu. Merc only listed the 7.

Now to find a Tohatsu dealer. Not too popular in my neck of the woods.

 

[Sea Rider]

The standard factory delivered props on both 3.5 & 4/5 HP engines are usually medium pitched ones. It's not a matter to swap props blindly, will need to know achieved max wot revs while pushing any given load, only possible with a tach installed.

An alum OEM 6 pitch is the least pitch you'll find listed for 4/5 Tohatsu and rebadged engines, you can always re pitch it at a prop shop to a 5 pitch to pull wot revs up to run max wot revs if in need, engine will rev safely, once there can throttle much less, it's entirely up to you.

My 5 HP engine increased 1 K wot revs to max range going from a 3 blade 8 to a 7 pitch while powering a boat at fast displacement speed due to being hard to plane.

Happy Boating