finding the right prop

[shine]

looking for feedback on finding a prop...

My boat: 23 CC rebuilt a little lighter than stock. Yamaha F225 on a bracket.

First prop was too small; 13.75" diameter and 17 pitch aluminum, it ran too high RPM.

Second prop caviation issues; 15.25" x 19 pitch, but it was a vented prop (holes in hub at base of each blade).

The second prop performance was a little strange to me. While the first prop held a nice grip until the motor was trimmed up more than half, the second prop would cavitate at anything other than all the way down/tucked in. At slow speed it was tolerable (although I could feel it a little), when running anything over 4100 the venting really was noticeable. I was still able to get 6000 RPM and 40 mph - lightly loaded. 22 mph at 4000 into (we had at least 15 knt wind), and 25 mph at 3800-3900 down wind.

Another wrinkle: second prop hub diameter is 1/2" or so less than gear case. It stood out to me as not looking right. below is a picture. Im sure this could explain a lot of the cavitation/venting also, there must be a huge amount of suction generated by such a drop in diameter.





I sent the second prop back by UPS today and will see what the shop sends back for prop #3. Seems like a 18 to 18.5 with a 15.25 diameter will be just right

Any ideas on that hub diameter?

[76Red18]

Hub diameter is wrong. Exaust is either escapeing between the hub and lower unit or being excessivly sucked through the vent holes due to the decrease in hub diameter. Thats your cavitation problem.

I would try a 15 x 17 with the right hub diameter. That prop in the picture dosen't appear to have much cup ( Trailing edge of blade has a slight fold or "cup" to increase bite). Seacrafts like some cup in their prop. It provides stern lift. Stay away from a prop with cup on the tips. That can produce too much bow lift.

[ct9amr]

Post up on propgods.com and Ken could help out.
They also do this as a service and I will be trying them out soon.

[GodsReel]

i am running a 15 x 17 on 23 cc 225 yami , armstrong bracket, light load i turn 6000 and run @44 on yami gauges, i do seem to have little to much bow lift and and a little disappointed on hole shot , especially with a full load of fuel? might get the cupping checked . Maybe try a 4 blade for hole shot but don't wanna give up to much top end. Oh and also need to be able to stay on plane at a lower speed. I am also coming of a 23 with a 2 stroke 200 on the transom. Not trying to hijack the thread just giving you some feedback on what i am experiencing with a very similar set up and also looking for feedback myself. Are you using propgods?

[shine]

thanks for the link to propgods, once I get a proper fitting and non-vented prop I will get some good data and take it to them and buy a "perfect" prop and turn the other into my backup.

The second prop test was not worth much, with the vented and too small hub.

i am running a 15 x 17 on 23 cc 225 yami , armstrong bracket, light load i turn 6000 and run @44 on yami gauges,

thank you for that. I think we will be pretty close, the first prop I used was a 17 pitch but the diameter was smaller so my RPMs were even higher.

[Old'sCool]

I don't think there's one that covers all situations, kinda like the multi boat theory. I'm running a Solas 4 blade 17 on 23' w/Hermco bracket, 250 Yam 2s. Cruise high 20's-30, tops ~ 40 but holeshot is good and lower planing speed when rough. Typically ~ 2mpg. The 3 blade 19 runs faster and will hit low 5k rpms, holeshot is acceptable, but have to run a little too quick when rough.

[76Red18]

Hey Shine, theres nothing wrong with a little ventilation at the initial burst of throttle to get on plane. It helps the engine build rpm. Its easier on your motor to jump on plane rather then just easing it up.

[McGillicuddy]

I think Reelescape makes a good point regarding different props for different situations but finding a good all-around prop that covers 80% of your applications shouldn't be that tough. Most SeaCraft ccs need some stern lift from a prop.

I think this and all prop discussions would be a lot more meaningful if the props are identified including make, model or model number as well as material, diameter and pitch and number of blades.

Different prop shapes are designed to do different things.
Diameter and pitch are a part of the equation but with the wrong shape, cup, or rake, you're pulling wheelies instead of getting on plane efficiently.

Obviously in this group there will be differences as people have shifted cg around by moving tanks or batteries, or adding pilot houses or brackets, etc. Others lightened their boats dramatically by shedding pounds of wet wood replacing it with composites.

Shine, I think your f225 has a 4.75" gearcase, but double check that... PowerTech Props has some quality stuff at real fair prices. Maybe you prop guy carries their line. Check out the MQS and SCE models. they come in 3 and 4 blade and mimic Mercs Black Max and Yammies own Semi-Cleaver. Great stern lift and all around performance. Very informative site, too. www.ptpropeller.com

Godsreel, I think a 4 blade typical helps any SeaCraft with a big 4 stroke especially if the pointy end is riding too high. I don't recall if you're running a 4 stroke or not, but either way, I'd give up a barely noticeable mph or 2 @ wot for better hole shot, handling, and cruise efficiency every time.

Good luck guys and try to post your results and prop info when you get dialled in.

[eggsuckindog]

I will say as far as props the Stilletto I bought is awesome, very aggresive so be careful not to over pitch as it will be 300 RPM lower than the same as others, but it will hang with great trim response. Moving my motor up 2 holes this week, they are bad azz, which will put me at least 2" above hull bottom. I will report back after the change, its about 1" now but I never cavatate even trimming way up so up she goes.

[junior11]

I am going through the same thing. I have a yamaha saltwater series 17 by 15.25 three blade. The engine is an F250. Also on a bracket. It seems as though my cruise is at 4500 at 26 kts burning 10.5 gph. I haven't really pushed it in good conditions yet to see the top end, I will let you guys know though.

What was weird is I went out straight into 2-3 footers, and a 15kt wind the nose stayed down the ride was dry and smooth, no porposing at all. I was thinking man I can't wait to go down sea and let it scream. I turned down sea and the but was up and down, and I lost 3 kts at the same RPM. Ride became a little wet also. Also as soon as I drop below 4300 RPMs the boat is flirting with coming off plane. I am a little bothered by how high I have to keep the RPMs to stay on plane. I am seriously considering the 4 blade prob...