I have a very cheesy inboard set Id like to correct in the cheapest way possible.Here is my set up and what I'd like to accomplish.

14x3 welded aluminum hull.It was an older thick riveted hull and the bottom was cut out and replaced with a 3/16" aluminum sheet so its now a really heavy hull but moves and rides smooth.

13 hp kohler command direct drive with a prop for an 18 hp that was turned down by hand.No tach but the rpms are near 3000,boat goes thru some badass stuff without an issue and speed of 22mph.

Strut is the steepest angle I have ever seen.Havent measured it yet but its close to 20 degrees id I had to guess.

Problems I have.
The aluminum strut weld cracked,worn lower strut bearing.
Massive angle on motor.
Boat was put together poorly......however it gets the job done and I got it cheap and for what it is its performance is impressive.

My want to do list:
10 hp diesel that puts out 20ft lbs at 1500 rpm and 19ft lbs at 3600 rpm(13 kohler puts out 21 ft lbs at 3600 but a lot less at lower rpm's)

I have a very small manual transmission with clutch
2nd gear is 2:1,reverse is 2:1,3rd is 1:1
I have new aluminum to fabricate a new strut with a 12-14 degree angle to lower the engine angle......which for the diesel it don't matter cause it has no carb or float.

questions are:

which would be the better performer just to fish out of and make it thru some rugged areas.All soft bottom very lil water.

1:1 forward with the correct propeller with a 2:1 reverse?

2:1 forward with 2:1 reverse with a larger prop?

Im impressed with its current direct drive performance but I have this transmission already and its not too much more effort to use it.Transmission is from a 10hp diesel tractor and has twin clutch disc about 6" round and grabs hard.

so will a prop for a 1:1 out perform a 2:1 set up under working conditions......not really concerned about top speed.anywhere near 20mph is plenty for this small engine.



I know.....just get a surface drive.I considered pluuging the hole in the bottom and building a surface drive but I like inboard boats with reverse.The boats transom is 3/16" as well.

Oh and people on other engine forums compare these 10hp diesel engines to larger 14-16 hp engines performance cause of the flatter torque curve it produces.
Thankxz for your help.

here is the lil transmission,I like showing it off cause its cute.It has a dual disc clutch and the output shaft is 1" 18 spline which no coupling exist for it so the output shaft will be removed and machined to 7/8" or 3/4" and keyed to adapt a coupling.The transmission is next to the 10hp diesel which is about the same size as my 13hp kohler gasoline.

info on your mudboat

viewtopic.php?f=4&t=34626

info on your mudboat

viewtopic.php?f=4&t=34626

I have owned many inboard mud boats and almost every strut was at 15 degrees. that's around the best of both worlds for a inboard! and I personally would not put a diesel in one unless it was one of the 23 hp v twin ones , but that's just me!