merc 25hp prop selection

[naughtybynature]

hey guys and gals, does anyone have expereince with propp selection for a 25 merc? i have a stock 13 pitch that spins 5000rpm at WOT, and a 18 pitch chopper that spins 4500 at WOT. i really like the rooster and the attitude of the boat with the 18, but i have to trim it so high that i am loosing so much efficiecy. what i want to do is be able to spin the stock prop to 5500 or 6000 rpm. has anyone done this with my motor? how much pitch did you take out to see this kind of increae? is it safe to run the motor at this rpm? (book sez 5000-6000rpm) <br />i am running the motor on a 12ft mod vp hull that i made, wieghs about 300 pounds. top speed with current setup:<br /><br />13 pitch ---- 35 mph<br />18 pitch ---- 38 mph<br /><br />any help with this would be very appreciated.

 

[naughtybynature]

Re: merc 25hp prop selection

oh ya, here is a pic with the 18 pitch on, all trimmed out and dancin! yahooo

 

[Spidybot]

Re: merc 25hp prop selection

Hi. I think I know exactly what you need: Information. <br /><br />When you play with choppers you should pay attention to the motor mount hight on the transom + trim angle.<br /><br />Here's one place to learn it: http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=17;t=014920

 

[FlyBoyMark]

Re: merc 25hp prop selection

"+" you need to keep the engine at about 6000 RPM for it to produce 25 HP. Merc 25 is rated 25 HP@6,000 RPM. Less than that, your not getting 25 HP.

 

[naughtybynature]

Re: merc 25hp prop selection

thank you for all the help. the info was very good on props. i pretty much had a good understanding on must items. what was really bugging me and i could not get any info was where my engine should be running. the mauual sez 5000-6000rpm ??? that is alot of rpm there and potential speed. mark you have solved my problem. are you speaking from experience that it is ok to run a 93 25 merc to 6000rpm? if my stock 13 prop only spins to 5000 should i be concerned, or was that the desired rpm for that pitch. going to an 11 will only see me about 5600 acording to the info plus i wan to add some cup to help carry the bow, wich will loose some rpm, why am i falling short? thanks for your help! i guess i will stop using that 18 pitch as i may be cuasing damage due to the 4500 rpm max i can get with it. will miss that rooster!