Inboard Issues

[mbd]

It's a Yanmar 2GM. 13HP, 3400 RPM, and 15HP at 3600 RPM max.

I also have a three bladed prop. (See pictures)

"Will your tach read above 2100rpm when not in gear?"

This is the million dollar question for which I am ashamed to admit, I have no answer.

I didn't realize I was in trouble until after the season and I was reading the manual while winterizing the engine. I'm pretty sure it does - at least the engine revs pretty good when in neutral. I just never looked at the tachometer while doing it.

[Mike Goodwin]

You have one blade too many on that prop . No way you can turn a 13x11- 3 blade with 13 hp unless it was in a 400lb skiff . At 2100 rpms your are not even getting 13hp. That is a huge prop for a small boat .

My figures were for a 2 blade 13x11 , that extra blade needs more hp to spin it.

It is probably a motor boat prop too , and has huge surface area .

Get a 12x6 sailor prop (2 blade ) and you will be happy for the rest of your life .
You will sail faster too (less drag )
1216 shaft rpms should give you 6+or- knots with a 12x6 ( 6" pitch ) prop , so if you throttle back a little 5.5 knots is easy .
You know you can have props re-pitched , so get a 2 blade that is close and try it and if it is not exact either pitch it up or down until you can get 5.5knots at 2800 rpms .
There are a lot of other factors involved , but this gets you in the ball park .
I have re-proped dozens of boats , half were right on the 1st try and the others took one more pitch change to get close enough . planing motorboats are a lot harder to get right .

[Mike Goodwin]

BTW , the Vetus coupling doesn't add any length to the drive train .

[mbd]

Mike, thanks as always!

BTW , the Vetus coupling doesn't add any length to the drive train .

I'll get back to you in the spring on this one.

At 2100 rpms your are not even getting 13hp. That is a huge prop for a small boat.

This is where I started. My local boatyard said the same thing and I was planning on downsizing until I ran the figures through the prop calculators.

I suppose one route to go, after rewiring the tachometer, is to find a smaller cheap prop somewhere and see how that does next season. I'd hate to muck it up so bad that it'd force a haulout to replace the prop - the season is short enough as it is.

Thanks again.

[mbd]

BTW, I'd really like to hear from other Ariel/Commander/Triton inboard owners what their setups are. (Engine HP/RPM, transmission ratio, prop size/pitch)

Any info appreciated!

[Mike Goodwin]

What prop calculators did you use ?
I did the same thing and you see what I got .

[mbd]

My engine specs:
Yanmar 2GM 13 HP @ 3400 RPM, 15 HP @ 3600 RPM
Trans: 2.62:1

Michigan Wheel: http://miwheel.com/MIWheel/PropAnaly...is/InboOne.asp

Results: "Mike, according to my calculations, your current 13 x 11 three blade prop should allow the engine to reach its maximum rated RPM (it is nearly the same as the theoretical size, based on an engine rated at 15 HP @ 3600 using a 2.62 to 1 reduction gear, and a top speed of 5.5 knots)... I am reluctant to suggest a 13 x 6 or 13 x 7, which it appears is what you need based on the reported current performance and propeller size..."


Gori Propeller: http://www.gori-propeller.dk/

Results:
Calculated Propeller
Two Blade : 15" x 12" RH
Three Blade: 15" x 11" x 3 RH
Warning: There is an unusual big difference between the estimated hullspeed of your boat, your previous topspeed under power and the expected speed. The propeller sizing you get here might need modification, please contact us before ordering.


Carl's Sailing Calculator: http://www.image-ination.com/sailcalc.html

Results: This was an easy one, no emails, no browser forms, just punch in the numbers. Bottom of the page, pick your boat, enter HP and prop type. I entered 15 HP and a 2-bladed prop and got 21.4" on this one!!

Something is not adding up. I must be doing something wrong here...