X dimension and prop size on my 19 cc aquasport 150 johnson crossflow

[jy118lfd]

I had it out today and tried a 15x17 prop that I had lying around. 5100 rpm and 44 mph holeshot was unreal. My question is I can trim all the way up and not lose prop bite. It knida rooster tails and you can see the water spray from the cav plate come out at a 45 degree angle. I still have 2 holes to go up How much rpm can I expect to get by raising the motor? Also the 15x 17 has no vent holes in it should I add these?<br /><br />I also checked my tach with a fluke meter and it reads right so I know rpms are accurate. <br /><br />I will also say that the 15x 17 is an omc prop and the other props I tried were hustler, all alumnium. What is funny is that I went from a 141/4 21 to a 19 pitch and did not change rpm at all. The hub seems rather large and it looks like it could create quite a bit of backpressure on the exhaust. I dont know if this was the problem but to go to the 17 and get 900 rpm seems like alot. <br />If I can get it to rpm right I will be tempted to go and get a stiletto to try for better bow lift <br /><br />Its a 78 150 crossflow 20" shaft

 

[jy118lfd]

Re: X dimension and prop size on my 19 cc aquasport 150 johnson crossflow

Bump

 

[Silvertip]

Re: X dimension and prop size on my 19 cc aquasport 150 johnson crossflow

Propeller performance is dependent on a number of things and most of those things are discovered by trial and error. Whether or not you add vent holes is one of those. Try it. If it does nothing for performance, no big deal. If it hurts performance, plug them. Cupping vs non-cupped affects RPM. Blade design affects RPM. Diameter affects RPM but not as much as pitch. In your example, you went from a 21 pitch to a 17. If you figure 150-200 RPM per inch of pitch change you should see 600-800 RPM increase. I suspect you were severely overpropped with the 21" prop. The numbers you provided would indicate you were only turning 4200 with the 21".

 

[walleyehed]

Re: X dimension and prop size on my 19 cc aquasport 150 johnson crossflow

If you already have good hole shot, don't drill vent holes....<br />You need to raise 1 hole at a time until you either blow out before reaching the trim level desired (needed), or obtain the results you want.<br />A jackplate may be needed for best performance, and shoot for 5500 as a minumum max RPM WOT.

 

[jy118lfd]

Re: X dimension and prop size on my 19 cc aquasport 150 johnson crossflow

Thanks for the replies. Upinsmoke You are right I was at 4200 with the 21 and 19 pitch and the change to the 15 x 17 netted 5100 rpm at 44 mph fully trimmed. I have winterized the boat now but just wanted some suggestions for spring. I will raise the motor one hole and try again. I really can't wait to test again I really think it is fun tring to get the most from a boat and motor! Not only for performance but for longevity also.

 

[walleyehed]

Re: X dimension and prop size on my 19 cc aquasport 150 johnson crossflow

you'll gain "approx" 150 RPM per hole up, and stay with the 17 for 2 reasons for now....Base-line info and 5100 ain't high enough R's for eng longevity.<br />p.s. winter sucks don't it...

 

[jy118lfd]

Re: X dimension and prop size on my 19 cc aquasport 150 johnson crossflow

Yea I am shooting for 5800. I really think it needs to go much higher by the way the spray comes off the cav plate at wot and how it will not lose bite at full trim. I need to change the trim motor so I guess I will raise the mount then. <br /><br />Winter really sucks especially with a center console Hard core fishing to say the least

 

[jy118lfd]

Re: X dimension and prop size on my 19 cc aquasport 150 johnson crossflow

Went out the other day. I raised the motor one hole now it is one hole away from the highest setting. My problem is this; Thae last time I went out I had low fuel and one person now it has a full tank from winter. Plus one other person. 5000 rpm and 40 mph. i was just wondering how much rpm can you lose with weight. From light load to a moderate to heavy load. I will go out again to run fuel out and retest.

 

[Dhadley]

Re: X dimension and prop size on my 19 cc aquasport 150 johnson crossflow

Be real careful running hard on last years fuel. We dont want to be putting pistons in when we should be testing. If you insist on running it out just be real easy and patient. And dont go topping off with fresh fuel thinking tht will solve the problem.

 

[jy118lfd]

Re: X dimension and prop size on my 19 cc aquasport 150 johnson crossflow

But I thought if you store it with a large tank ie:40 gals built in, to store it full with stabilizer?