F-115 Possibly Mounted Too High?

[Jersey Jim]

I could really use the help of 1801 owners with Yamaha F-115's. On the trailer I notice my anti-cavitation plate is an inch or so higher than the scarboard plug at the keel. When underway I can see my drain plug. According to Yamaha's OB manuals, they recommend the AV plate be level with the lowest part of the keel.

My O.B. bracket has two unused bolt-holes Above my mounting bolts, and one unused hole Below my mounting bolts. I have room to lower the O.B. 2 more notches. When trimmed out a bit more than usual I hear the prop cavitating. Hull & O.B. are 2002.

My question is....is my mounting position what everyone else uses on their 1801's?

 

[DaleH]

According to Yamaha's OB manuals, they recommend the AV plate be level with the lowest part of the keel.

That is a recommendation only.

Try this, get on plane and cruise and trim out 'til the prop ventilates, and then drop the trim a tad to eliminate the venting. Can you steer OFF your course OK? Does she lose the bite when crossing wakes or chop? If not - you could be fine as is!

Now, to do ANY fairly tight turn, one typically MUST drop (via trimming it IN) the motor and tuck the OB down.

Kudos to whoever set up your Yamaha.

Agreed !

IMHO too, most boats have the motor mounted wayyyyyyyyyyyyy too deep!

 

[Jersey Jim]

Thanks for the good info. I'll try the steering/venting test next time out. I had no reason for alarm, other than the mounting not being consistent with the manual's recommendation. And also that in rough seas the prop cavitated when attempting to trim more than usual. It's reassuring knowing that another 1801 utilizes the same mounting hole out of the four (2nd from the highest).

Correction: My AV plate is not an inch higher than the plug as originally stated. I meant to say that it was an inch above the keel.

Jim

 

[skipperhub]

I have a 2002 2520 with twin yamaha 115s on an extention. I am also equipted with a couple of electric trim tabs that look to be 12 by 12.
My presumed problem is that the boat seems to be ploughing up a lot of water at the stern with the trailing edge of the extention dragging about an inch deep in the water.
My trim tabs, fully extended, seem place the outer most edges at about 1.5 to 2 inches below the bottom edge of the transom.
I have seen comments about newer models having much larger trim tabs from the factory.
It would be fairly easy for me to relocate the outer end of the hydraulic cylinders higher up on the suface of the tabs which , in turn, would push the trailing edges of the tabs deeper ino the water.
I would also be willing to have a whole new set of larger tabs installed if that is the best solution to the problem.
I am assuming better fuel management with a better plane on the few occasions that I get over ten or twelve knots.
Any thoughts?

Skipper Hub

 

[Porkchunker]

You have the same problem I had...too much weight in twin F-115s for the smallish 12x12 tabs. She is butt heavy, and the OEM tabs can't push the bow down.

Some have gone to wider tabs. In my case, I went with SS plates mounted to the bottom of my anti-ventilation plate. Similar to a Hyrdofoil, but stronger. Mine are by Cobra (Cabela's sells them), but Permatrim also makes them.

Somewhere around here is a thread with pics of my plates.

Dave

aka

 

[Porkchunker]

Here is a thread that shows the Cobra plates:
http://www.classicparker.com/phpBB2/vie ... ight=cobra

Dave

aka