Plane faster

[will941s]

I have a 14' BayRayder (fiberglass side console, v-hull) with a 25hp merc long shaft, 2-stroke. Heres the deal. Got the boat, tried it out myself....ran like crazy, fast...good plane. Decided to move both batteries to the back...went out with another person...took forever to plane, had to the person to sit on the bow...then took forever to plane. Put on a 4-blade adjustable pitch prop (had 3-blade aluminum, 13 pitch) and went to testing. Moved the one battery to bow, with the anchors. Hard plane. Brought the motor in a few holes...worse, out a few holes, worse...then found the max RPM at 13 pitch with new prop (about 3000 rpm) in the middle. Then went to taking some pitch away, at a 10 pitch now and with myself runs like a champ...about 5700 rpm's. With another person still takes time to get on plane, will get to 5700 rpm's though. Took hydrofoils off the motor....a little faster plane. Now....heres where I am. I got the rpm's right, the pitch is right, the balance is right, boat rated for a 30 max...has a 25, so it's good there. Without hydrofoils it does better, still slow to get on plane with another person. The bottem of the boat is almost level with the plate right above the prop....I think its supposed to be level with the plates above that right? So if thats the case, then maybe the motor is sitting too high and needs to be lowered....would that improve the plane situation? Like it can't get that good shot of water to grab to shoot it up to the surface. Thanks for any help.

 

[Silvertip]

Re: Plane faster

You are stating the relationship a little backward. You adjust the motor up or down one hole at a time to achieve maximum performance. That usually means the AV plate is "higher" than the bottom of the boat by about 1 inch or so. Keep going up until there is no more improvement -- but you need to be careful that you don't go so high that the water pickups fail to draw cooling water.

 

[will941s]

Re: Plane faster

I put the motor in one hole at a time, it got worse. Then I tilted it up one hole at a time til it lost performance. Where it's at now is the "sweetspot". It has the best rpm's, torgue and get up and go. The plate above the prop is pretty much even with the bottem of the boat. The plates above where the lower unit mates with the midsection is about 5" above the bottem of the boat. I was wondering if the motor it's self is mounted too high, and if I need to drop the whole motor down a few inches, to put that prop and the lower unit a little deeper in the water. When it's running basically the water flow is between the plate above the prop and the prop...not a whole lot of room for play there. Your thoughts?

 

[kenmyfam]

Re: Plane faster

How about a photo to show us. Sounds like the motor should be moved up a hole on the transom bracket.

 

[will941s]

Re: Plane faster

I will post some pics on here tomorrow.

 

[will941s]

Re: Plane faster

This the location of the cavatation plate to the bottom of the boat. And the location of pin in the tilt system. In that setting the boat operates the best.

 

[will941s]

Re: Plane faster

So I went searching and found a Mercury engineer website that showed the correct postion of all Mercury outboards. The cavatation plate on the motor is at it's peak position at 1" below the transom. Mine is even or slightly above that position with the motor the way it is. They also mentioned "dirty water", the turbulent water caused by the boat passing through it. If the motor is too close to the transom, it's possible for the prop not to "bite" due to passing through water that full of air, moving in all directions, and boiling. Sooooo....I guess my options are, drop the motor an inch (I can get that by shaving leftover fiberglass molding on the top of the transom), or setting the motor back a few inches. Thoughts?

 

[kenmyfam]

Re: Plane faster

Picture 1 looks like you could come up a bit. Make sure you are getting enough cooling though.
Look at the cav plate when on plane as well. Where is it then ???

 

[will941s]

Re: Plane faster

On plane you can see the whole cavatation plate. The water flow is going under it and everything above it is dry.

 

[will941s]

Re: Plane faster

Thanks everyone for all of your help, iboats is a great forum with a lot of great ideas and all the know how you need. I got the problem worked out, after burning a tank of gas and changing the set up multiple times. I went down to a 10 pitch prop, and installed the hydrofoils again. Moved a little more weight to the front (anchors) and BAM! Planes and goes. For the first time I had my wife to sit beside me instead of the front...planed like a dream. By myself I think I can run 11 or 12 pitch but even by myself with the 10 pitch it will still run about 35. It's a v bottom boat so I guess naturally it's going to be a little slower. I gave my dad my 14' jon with a Merc 25, 2-stroke and he can pass me by about 3 mph. But that a flat bottom and the take off power will almost throw you out of the boat. Thanks guys.