Prop advice... need more stern lift... Add hydrofoil?

[pjbrownva]

Originally Posted by SkunkBoat

This is from an old post

"It's a Suzuki 3 blade stainless 14 x 20. It has vent holes at the base of each blade. It's the original prop that the dealer fitted when he installed the motor. I run fairly heavy, with lots of rods, gear, anchors, coolers, and always 30 -55 gallons of gas. The hard top adds some weight too. At WOT, light, with motor trimmed up perfectly, she will get to 6000rpm and ~38mph. But I rarely do that. When I'm in a hurry I'll run at 5600 rmp, just shy of WOT.


Do a search on the Tag "DF140" for more info.

zukes have a 2.5:1 gear ratio. They need a big prop. I suspect you have the 17" prop trimmed in too deep to keep it from overrevving. 17 is too small.

You should be able to run fine with no tabs and definitely without a fin.

And the manufacturers have a range for WOT for a reason. Don't stress about getting to the max of the range. Get the boat to perform well out of the hole and cruising.
Testing should be done without tabs and fins and crap.

Thanks for all of the info, @SkunkBoat. I've taken a break to hibernate for part of the winter. :-)

I plan to get back on the water in March, and continue this tuning. I think you're right about needing more pitch and raising the motor height. I *think* I have a 19 pitch Solas 3 blade SS that I ordered and tried for a short while.... so it's basically new. I guess I'll go back to that, raise the motor and report back.

'Til then, wish me sweet dreams! (hehe!) Hibernating is fun!

[pjbrownva]

Originally Posted by spareparts

generally speaking, the higher up you can run the engine, the more efficient it will perform, but with everything, there will be trade offs. Easy way to check it, have someone run the boat in a normal fast cruise and trim position, look over the stern and see if you can see the anti-ventilation plate on the engine(the thing you bolted the fin to). It should be just out of the water at a good fast cruise and proper trim position. The fin should be skipping across the top of the water. Be careful, don't fall in. If you have time to play with it, raise the engine up till it blows out in turns then go one hole back down. The higher you raise it, the less leverage you will have

Here's an update.

I ran WOT with a buddy driving, and the anti-cavitation plate was about 3 inches below the surface (!!!)

I bought a used atlas jack plate with a 12" set back.

The jack plate will make it a lot easier for me to fine-tune the engine height.
I know it needs to go higher. I also know that the setback from a jack plate tends to make the motor behave as if it were higher.


I haven't mounted the jack plate yet. Soon (hopefully).

-Philip ***127866;

[spareparts]

12 inch is a lot of setback, usually only use them for bass boats or when the transom interferes with the engine. You ma have to move some weight around in the boat to help balance it. Normally, when you use setback, it allows you to run the engine higher, rule of thumb, every 4 inches back, 1/2 inch up. So with that setback, you need to mount the engine even higher. Good thing is, having the adjustability will make it easier to get the height right. Downside is, the further back you go, the less stern lift you have(does wonders for bow lift) and it may make it harder to get on plane, especially at lower speeds

[pjbrownva]

Originally Posted by spareparts

12 inch is a lot of setback, usually only use them for bass boats or when the transom interferes with the engine. You ma have to move some weight around in the boat to help balance it. Normally, when you use setback, it allows you to run the engine higher, rule of thumb, every 4 inches back, 1/2 inch up. So with that setback, you need to mount the engine even higher. Good thing is, having the adjustability will make it easier to get the height right. Downside is, the further back you go, the less stern lift you have(does wonders for bow lift) and it may make it harder to get on plane, especially at lower speeds

Thanks for the info, Spare Parts. I guess it had it all wrong....

So, the good news (really good) is that the 12" setback on this atlas plate is a 6" set back plate with 6" spacers, so I can unbolt the spacers and run it with only 6" setback if necessary.

Still, I think I'll try it with the 12" setback and see.... plus, I use this boat occasionally in a lake in MASS that shallow AND rocky bottom, so being able to raise the motor is a good thing in those cases.

More bow lift isn't a good thing, but well see how she goes!

For weight, I was thinking of moving both batteries to under the passenger seat... but then I thought about it (and looking at the work and additional cost for runs of marine grade cables)... it seems that maybe I should go with some LiFeP04 batteries instead. I've found 2 or 3 brands that now make models designed to put out enough current to use as a starting battery... and each 60 Ah LifeP04 battery weighs only about 15 lbs... so that's a HUGE weight reduction!

Any thoughts on the topic are appreciated...


P.S. -- A bunch of new parts came in this week... I'm not gonna post about them yet. I wanna get them installed w/ some photos, and then I'll post a new thread for each mod / addition.

-Philip

[spareparts]

take the easy way. Fill a cooler, invite some fat friends, have them move around in the boat, from front to back, move the cooler as well, and see how it changes its running attitude