Help with motor positioning???

[steve forsythe]

My boat will not stay on plane under 3500 rpm's. It might be underpowered at 23 feet with a 200. It takes almost full power to get on plane and then you can back it down but only to 3500-4000. Should i get my prop checked for size and pitch? It is stainless but i have no idea the size or pitch. The shop raised the boat on the jack and that helped a little but how do i know if it is in the right place? It is at 5500-5800 at WOT, and i am not sure if that is optimum for my motor or not. It is a 2000 carbed Merc 200hp saltwater series. If anyone knows anything to help me, let me know. Thanks.

 

[JB]

Re: Help with motor positioning???

Howdy, Purse Snatcher.<br /><br />What boat do you have? Do you know what HP it is rated for? Has it ever performed differently?<br /><br />Your engine is probably properly propped if you can get it to 5800, but your boat may be underpowered, too heavy, have a draggy bottom or just be a poor design.<br /><br />Let us know what boat you have and it's power rating.<br /><br />Red sky at night. . .<br />JB

 

[steve forsythe]

Re: Help with motor positioning???

It is an irvette from Irvette Marine. Not a real large boat maker but a good design ive been told. It has a deep hull and is real dry in rough seas. How do i find out what it is rated for. I think 200-250hp. One tip you might be able to give me....do i want the motor trimmed all the way down when i am trying to get up on plane? Also, when trying to stay on plane at lower rpm's, do i want the engine trimmed all the way down or up a little?

 

[JB]

Re: Help with motor positioning???

Howdy, Purse Snatcher. I didn't even think of trim. Glad you mention it.<br /><br />Once you get her on plane, trim her out a bit. That should raise your bow and reduce the contact area, increasing speed. Back off the throttle a bit and trim her out a bit more. <br /><br />It will take a bit of experimenting to find the best trim for your loading on any particular day. <br /><br />If your boat starts to porpoise you are trimmed out too much. That will certainly reduce the rpm you need to stay on plane. <br /><br />You may find that you can rev her well past the 5800 you were getting before. If so, go to a longer pitch prop.<br /><br />Let us know how it works.<br /><br />Red sky at night. . .<br />JB

 

[steve forsythe]

Re: Help with motor positioning???

Thanks JB. If she goes too high do i need to change the pitch up or down to lower it. Also, can someone measure the pitch and then adjust it accordingly? Thanks again.

 

[JB]

Re: Help with motor positioning???

Howdy, PS. Up. 1" for each 200 rpm you want to reduce top rpm.<br /><br />Red sky at night. . .<br />JB