Nissan 3.5 B2- more power or less prop slip?

[gfp]

I'm using this motor to push a racing sailboat out and back to the course. It yields just under 6 knots at 4800 rpm with a 7 inch pitch prop at WOT.

Is there any way to coax more power out of the motor? Or effectively more speed out of the boat by reducing pitch slip?

With a 6 inch pitch prop, it runs over the max rpm for the motor.

Thanks, GP

 

[Sea Rider]

Re: Nissan 3.5 B2- more power or less prop slip?

The engine parameters are : min 4,200 max 5,300 at wot, a 6" prop will push a bit upwards your actual 7" rpm's , sailboats are heavy, test both props and check which one gives better end speed with a GPS, don't go over max rpm listed for that engine at wot. Is your sailboat as heavy as a J-24 ? You only have 4.5-6-7 pitch props to choose from.

Happy Boating

 

[gfp]

Re: Nissan 3.5 B2- more power or less prop slip?

Thanks Sea Rider,
I own all three props. The 6 pitch pushes the wot rpm about 50-100 over the limit with no real speed increase either through the water or on the gps.

It's a J -80, so about as heavy as a 24 but more easily driven through the water.

GP

 

[Sea Rider]

Re: Nissan 3.5 B2- more power or less prop slip?

Pushing heavy sailboats and going 3/4 to full throttle seems to make no better speed difference at all, better throttle down, drink some beers while heading to your racing course. What happened with the 4.5 pitch prop, rpm's went higher than with 6" ? Asume you are using a induction tacho to wot test ? Conclusion: which of 3 available pitch props will you continue to use, standard 7" factory delivered or other 2 ?

Happy Boating

 

[gfp]

Re: Nissan 3.5 B2- more power or less prop slip?

I'll repeat the prop tests this week and post. Yes, inductive tach. Interestingly, the prop wash looks pretty good for something that calculates as more than 50 percent slip.

If we start drinking the beer on the way to the race course, we race too slow.

 

[pvanv]

Re: Nissan 3.5 B2- more power or less prop slip?

Remember your math, and the rules governing hull speed for displacement hulls. You have reached the max boat speed that you will get from this combination. Changing pitch will allow the motor to run a little faster or slower, but you are approaching hull speed, and that's all that wee 3.5 is going to give you.

 

[gfp]

Re: Nissan 3.5 B2- more power or less prop slip?

Thanks Paul.
We are approaching hull speed which is the target (~6.5knots). We are not trying to get on a plane, just optimize performance with this set up.

We have a nice big A sail for when we want to plane.

GP

 

[pscrabber59]

Re: Nissan 3.5 B2- more power or less prop slip?

Thats about max power you get from that motor, I had a 93' Nissan 3.5hp that was used as a back-up motor for my heavy 14' fg-fishing boat. Had to use it one day when my main motor went dead and it took me about 45mins to go about 3miles to the boat ramp. Solved the slowness by selling the Nissan and buying a 6hp.

 

[gfp]

Re: Nissan 3.5 B2- more power or less prop slip?

I repeated the prop test. The 7" pitch gives the best results, highest speed(~6kts) at around 4900 rpm. Both smaller pitch props will allow the engine to exceed the 5300 rpm limit with no increase in boat speed, in fact the 4.5" prop will only reach about 5kts@ 5300 rpm.

Sticking with the 7" prop.

 

[Sea Rider]

Re: Nissan 3.5 B2- more power or less prop slip?

That's fantastic, was planing to change (14) J-24 3.5B2 L engines factory delivered with 7" pitch props for 6" ones, hopefully did not. Nice to have all 3 available pitch props so to experiment at sea using an induction tacho. Thanks for testing them all and sharing your experience; plainly in agreement, great little engine.

Happy Boating

 

[gfp]

Re: Nissan 3.5 B2- more power or less prop slip?

Happy to contribute. Great engine.

 

[Sea Rider]

Re: Nissan 3.5 B2- more power or less prop slip?

For the gurus, is it possible to lube the shift lever side that slides against engine drive housing or inside shaft, where small o'rings are located by removing the shift rod lever cover & gasket ? With use, time, salt, factory grease tends to stick making shift lever quite hard to move into neutral/forward position. Have seen broken shifts levers because of this issue.

An idea: If you are experimenting gas leakage on lower tank neck specially in plain summer do to pressure buil up, remove fuel **** and wrap several turns of teflon tape to help fill the groove like in middle tank neck, ****'s neck will rest, seal & adjust much better on neck. Picture corresponds to 5 HP Soviet internal engine but will work fine on 2.5, 3.5 tanks.

Happy Boating

 

[TOHATSU GURU]

Re: Nissan 3.5 B2- more power or less prop slip?

The B model was specifically designed so that the shift handle assembly could be accessed for easy maintenance. From start to finish, five minutes.

 

[Sea Rider]

Re: Nissan 3.5 B2- more power or less prop slip?

The B model was specifically designed so that the shift handle assembly could be accessed for easy maintenance.

TG, nice to know, asume by removing the shift rod lever cover & gasket, right ?

 

[TOHATSU GURU]

Re: Nissan 3.5 B2- more power or less prop slip?

Correct, then remove the split pin that holds the lever to the shift rod, remove the shift lever and clean.