go up 1" on pitch? or cup my prop?

[Merc40fisher]

hey guys, I have a flat bottom aluminum boat(16x48), welded in aluminum front and back deck and small console for steering wheel and controls. My motor is a 2005 mercury 40 3cyl, 2 stroke. I have a stainless 12 pitch prop that came with the motor thats been on there since 05. My RPM at max speed is around 5800 + or - 100 depending on conditions. The motor is rated max at 5500, I usually get it on plane and trimmed out then back it down to 5500 and cruise like that, been doing that since i got the motor. my take off and max speed are pretty good, (33 MPH with 2 people), but my handling is HORRIBLE!!!!, a wide bend in the river... back it down, trim the nose into the water and hope for the best. if its a sharp bend.. you have to slow it down all the way to brake plane so you can make the turn. completely unacceptable for my new fishing spots. Im in the market for a new prop now and no boat shops around here want to help. my question is, should I go up to a 13 pitch prop to lower my RPM and call it good? or should I cup my 12 i have now? my main concern now is the handling. This thing handles like a hover craft in turn, you can feel it get up on plane side ways then you just slide. no bite from the motor at all. So from yalls experience, whats the best thing i could do? id like to keep my speed and acceleration decent, but i have to have better bite in turns. Thanks a lot.

 

[Frank Acampora]

Re: go up 1" on pitch? or cup my prop?



Prop 'aint gunna help the side slip. You need to attach deep strakes, a deep keel, or a turn fin to the bottom.

Cupping will reduce RPM about 200 and will "Bite" the water better, but it won't stop hull handling problems.

I need to do the same with this flat bottom boat only I don't need to actually come off plane, just slow down half way.

 

[Texasmark]

Re: go up 1" on pitch? or cup my prop?

If you were ventilating and sliding then yes on cupping. You said nothing about ventilating. Surprised the usual ribs that Johns have aren't enough to prevent side slipping. Course 33 with 2 people in a John is moving right along and could render them somewhat ineffective. Problem with fins is where to put them and what is there in the hull for an attachment point? What problems would the fin cause in beaching? What problems in loading on the trailer? Sounds like a rock and hard place thing.

Mark

 

[phillnjack2]

Re: go up 1" on pitch? or cup my prop?

first off you need to learn to drive the boat and anticipate the bend a lot quicker.
Now changing a prop can dramatically change its handling !!!
I have a 12x23 that is on the pojnt of dangerous for handling and yet its little bother that 13x19 bites and handles great.

on a 40hp merc I would be putting a much bigger prop for top end speed, at least 14 pitch and cupped to give 15 inches of pitch.
the 5800rpm is NOT going to hurt your engine in the slightest though, they can run at 6500 no problems.

now what make of prop is it ? all different makes and types do totally different things, they grab different and run different .
the bow or stearn lift is also different.
Just because you have a 12 pitch stainless don't mean its good for your type of boat.

go look and see exactly what it is, get the numbers from it and the make of it.
I will tell you straight off though, if its a solas then that is the problem, they look nice and that's about it, they are very poor in many ways compared to lots of other brands of prop.

also how high is the engine running or how low ? where is the cav plate compared to bottom of the boat ?
try changing the heaight of the motor and see what happens with your normal load.
try moving stuff around so the back end is a touch heavier.

also learn to drift the boat for turns at high speed, its flat bottom so can drift real easy.

lot s of things to try, but first find out what exactly the prop is and diameter as well as pitch.

phill

 

[Merc40fisher]

Re: go up 1" on pitch? or cup my prop?

I already know how to drive my boat, and "learning to drift the boat at high speeds" doesn't work out very well when the edge of the boat starts hitting the water and jumping. Then it's a matter of time before you or your passenger flies out when it eventually digs in. The motor is set exactly where it needs to be according to the manual. A professional merc shop installed the motor itself and did a very fine job. There is some venting if you can get it to turn at low speeds. A lot more than I'd like. Over all performance of the motor is spot on. I just need some steering. I'm with Texas on the fins. I fish very shallow waters some times and underwater obstacles always pop up too. So the fins are out.

 

[Frank Acampora]

Re: go up 1" on pitch? or cup my prop?

See my private message to you!