trim angle @ WOT vs rpm, what size prop?

[ziggy]

reading the other thread brings a question for me. on my trisonic(listed below) i got about 4000rpm @ wot, trim down. useing a 14.25(?) X 17 pitch prop. well, as i start trimming up, boat rises out of water more, rpms increase, up to about 4500 or round abouts, top speed, highest rpm. then there's trimmed to high, where ya get ventalation and no speed increase or benifit from trimming up. so the question is where do i pick my rpm to get the right pitch prop?

 

[tommays]

Re: trim angle @ WOT vs rpm, what size prop?

z<br /><br />if you motor has no problems the only thing left is a prop with less pitch will allow more RPM<br /><br />you many not get the exact rpm with a stock prop as the next standard smaller one may be to small<br /><br /><br />tommays

 

[ziggy]

Re: trim angle @ WOT vs rpm, what size prop?

i think you saying that i should be looking at the lower rpm, trim down,bow down, as a guide to which prop i should use. motor seems ok to me. it seems pretty rapped up at wot though at 4500, trim up. i was thinking specs for wot for this motor was round abouts 3900-4300. the prop i got works fine. it's at the prop shop now, so it's a keeper. was thinking i need two props anyways to be a safe and prepared boater so was only thinking about what i should consider and am confused about which rpm i should be looking at. i guess i would have thought the higher rpm. bow high. im i looking at this proper pitch question wrong then?

 

[Bondo]

Re: trim angle @ WOT vs rpm, what size prop?

Your WOT, is when the boat is running as Fast as it will Go, Trimmed to the Ultimate in Clean Running Attitude.............<br /><br />Not Trimmed Under........

 

[Don S]

Re: trim angle @ WOT vs rpm, what size prop?

Bondo has it dead on.<br />You need to trim up, have trim tabs us and used only for side to side trim (Not bow up or down).<br />To find the proper up trim, start up till you get best rpm vs. speed. When you trim to high, your rpm will increase and speed will decrease and the boat will porpoise. Trim down just till the boat stops porpoising and you should be at best trim.<br />A little too low is better than too high as far as cavitation damage to the prop goes.

 

[ziggy]

Re: trim angle @ WOT vs rpm, what size prop?

sounds like i'm understanding correct to me. that's about the way i trim Don S & bondo. hightest speed, hightest rpm. no porpiseing. i'm thinking i want to bring my rpms down a bit. like i said 4500 seems a bit high for this 72' 165hp. perhaps next size steeper pitch prop. 18 don't seem to common, next question will be what a 19 does to it. want a ss prop too. less flex on ss i hear too. hopeing that it wouldn't load it up to much (under wot specs)& give me a bummer holeshot. time will tell. ie, when i get the bread together to buy a new prop. bet i got a bit of time too. thanks peoples.

 

[Doug Durako]

Re: trim angle @ WOT vs rpm, what size prop?

Zig---is your tach right? I ran a rig with the same motor and drive setup for 12 years and I never got more than 4200 rpm with trim all the way to the sweet spot.<br /><br />A 19 pitch, in theory, will lower your rpms by 200. (200 rpms less for every one inch increase in pitch)

 

[ziggy]

Re: trim angle @ WOT vs rpm, what size prop?

dd, well that sure seems like a reasonable question that i can't answer right now. winterized now ya know. best recolection is that i got it set at about 650-700 idle on a sears tach-dwell. seems like that dash tach said about the same. from memory. good point about a possible incorrect dash tach. and i will check that out a little better before jumping to conclusions. i just realized something the other day about my boat too. guess it'd been in the back of my mind but never clicked. i got the three button trim on the dash. someones been engineering on it befor i got it. i don't have any limit to my trim. in the past i've trimmed up pretty far. perhaps more than i should. can bring it up to where its ventalateing. wonder if i'm not bringing it up to much maybe. man do i need to inspect my drive, but in the yard it sits, drive on. also regaurding the rpm range. man it sounds like 4500 when i get it trimmed up, pretty wound up sounding for a 6 i'd think. so perhaps i just keep finding things to adress here it seems to me. B.O.A.T. ? oh well, i've only had this boat for half of last summer, so i got time to play and pay, opps, got that backwards, pay, then play. thanks, sure do learn a lot here.

 

[bigbrownbuku]

Re: trim angle @ WOT vs rpm, what size prop?

if the boat can achieve 4500 thats fine, just dont run it there. if you are happy with the performance ie speed, time on plane etc stick with that pitch. a day will come when you have an extra person and some extra gear or your kids want to ski. your engine will thank you for it.