Lowe FM175 porpoising issue - help

[coubi]

I have a Lowe FM175 with a mercury 115 four stroke that has a 15 pitch quicksilver aluminum prop. The motor is mounted on the 3rd hole down. When on plane and I start to trim up and the boat porpoises rather quickly the. The trim qauge is about 1/4 the way up or a little less. The motor also cavitates rather easily when turning. Is there anything I can do to help solve this issue. Thanks for you imput.

 

[Bondo]

Re: Lowe FM175 porpoising issue - help

Is there anything I can do to help solve this issue.

Ayuh,... Sounds like the motor is to High, try lowerin' it....

 

[coubi]

Re: Lowe FM175 porpoising issue - help

Ayuh,... Sounds like the motor is to High, try lowerin' it....

Thanks for the reply. Would you lower it 1 hole at a time or drop it the 2 holes I have left.

 

[oops!]

Re: Lowe FM175 porpoising issue - help

agree with bond-o

use your measuring tape and do some basic math.......

the anti vent plate should be even with the keel....that may be 10 holes.

 

[steelespike]

Re: Lowe FM175 porpoising issue - help

Try to keep it as high as possible.Is the prop in excellent shape?
Before lowering it consider a 4 blade prop.It will resist venting and my reduce the porpoising.
Increase hole shot and stay on plane at less throttle.Also may handle better both underway and at the dock.Before any changes get us your prop size and present max rpm and speed.

 

[oops!]

Re: Lowe FM175 porpoising issue - help

hey spike......im just wondering.....why change props first?. (understand bud this not a challenge to your wisdom)
in my humble opinion..... if he is blowing out in the corners.....he is high....so a prop wont help the height issue.

what are your thoughts bud?

 

[coubi]

Re: Lowe FM175 porpoising issue - help

hey spike......im just wondering.....why change props first?. (understand bud this not a challenge to your wisdom)
in my humble opinion..... if he is blowing out in the corners.....he is high....so a prop wont help the height issue.

what are your thoughts bud?

WOT on the mercury 115 4 stroke is 6400RPM. I hit 6200RPM with a top end of about 42 mph using a gps for speed.

 

[coubi]

Re: Lowe FM175 porpoising issue - help

the prop is a 15 pitch quicksilver aluminum prop. I don't know what the diameter is for sure, but probably about 13 1/2 give or take. It was what came with the boat

 

[coubi]

Re: Lowe FM175 porpoising issue - help

I was considering going to a ss prop. what is your thoughts on that?

 

[Shabah 182]

Re: Lowe FM175 porpoising issue - help

Buy yourself a set of Nauticus smart tabs for about 120 dollars and the porpoising will disappear! Worked wonders for my boat. There are lots of threads on them.

 

[5150abf]

Re: Lowe FM175 porpoising issue - help

If you are blowing out in turns the engine is too high and no prop made will fix that, drop the engine a hole and see what that does.

You can also tap the trim down when you are going into a turn to get the prop lower in the water and it shouldn't blow out then and you can still run the engine at it's current height.

Mine is set up like that, it runs fine in a straight line but will blow out in turns so I just bump the trim and it doesn't do it.

Porpoising is a product of too much trim, when it starts just back off the trim a little and it will quit, if your trim gauge is like others I have seen the bottom 1/4 is your trim range so you would be at the very top of the usable range at 1/4.

 

[steelespike]

Re: Lowe FM175 porpoising issue - help

hey spike......im just wondering.....why change props first?. (understand bud this not a challenge to your wisdom)
in my humble opinion..... if he is blowing out in the corners.....he is high....so a prop wont help the height issue.

what are your thoughts bud?

He had a couple of issues.Lowering the motor will no doubt stop a venting issue assuming no other venting associated problem.Lowering the motor will increase drag and increased prop bite could further agrivate porpoising.A 4 blade could likely eliminate porpoising and improve other handling issues that a simple though possibly free lowering won't address.

 

[shoestring]

Re: Lowe FM175 porpoising issue - help

prop "cup" really helps the vent/ cav. problems. those whale's tail ( I mean tale) bolt on planing aids can cause some porpoising issues in smaller boats as well. they seem to do what is intended and you can trim them out ok on glass but you hit some waves/ cross a wake, the waves start a little bouncing in the bow and the tail (tale) just seem to magnify it. not so much on heavier boats.

 

[oops!]

Re: Lowe FM175 porpoising issue - help

He had a couple of issues.Lowering the motor will no doubt stop a venting issue assuming no other venting associated problem.Lowering the motor will increase drag and increased prop bite could further agrivate porpoising.A 4 blade could likely eliminate porpoising and improve other handling issues that a simple though possibly free lowering won't address.

thanks spike......ill try that on my own rig

 

[coubi]

Re: Lowe FM175 porpoising issue - help

I have a Lowe FM175 with a mercury 115 four stroke that has a 15 pitch quicksilver aluminum prop. The motor is mounted on the 3rd hole down. When on plane and I start to trim up and the boat porpoises rather quickly the. The trim qauge is about 1/4 the way up or a little less. The motor also cavitates rather easily when turning. Is there anything I can do to help solve this issue. Thanks for you imput.

thanks for all the replies. I lowered the motor two holes and the motor cavitation plate is now withing 1/2 inch of the bottom of the boat. This solved the porpoising and cavitation problems. Also the hole shot is improved. Again thanks for all your replies.