Dingy Prop Size

[Jon D]

With all the discussion on dinks and motors, thought I'd throw this out as well. As I have said before I'm a believer in RIB with max HP for the size. We have a Caribe 9x with a Yamaha 15 2 stroke. Always had power but sometimes did not want to plane easily.

This year as part of the service process I replaced the prop and went down one inch in pitch [one size]. What a change. The boat just jumps on to plane with the three of us on it [me, Jill, Jetta [90 lb Giant Schnauzer] independent of where we are in the boat. Used to have to kinda watch weight balance -- not with the new prop. Also gives me better control so we can keep on plane but go slower -- a good thing .

[GordMay]

Did you change the Pitch, when you reduced the diameter?

[Pblais]

Having the proper propeller makes a huge difference. I went though that with my sail boat. The prop was too much and with the correct prop the boat motors faster and runs smoother at lower rpm's. Too much propeller is a bad thing on any boat motor.

[Jon D]

Originally Posted by GordMay

Did you change the Pitch, when you reduced the diameter?

sorry for the confusion -- diameter stayed the same went down 1 inch in pitch.

[defjef]

I am confused by this account. Yamaha sells a motor with an underperforming prop... or one which underperformed with YOUR dinghy?

What IS the relationship between pitch and "performance"? Is this a trial and error deal?

Jef
sv Shiva
Contest 36s

[Doghouse]

Not every prop is correct for the buyers use. A lower pitch will give you more power to get on plane, but you loose top speed. A higher pitch will give you more top speed, but at the cost of the ability to jump on plane. That is why some power boaters have 2 props, 1 for pulling skiers where you need a lot of kick, but little speed; and another for ripping the shirts off their "guests"...

[Jon D]

It is specific to the dingy.

These engines are typically prop sized for putting on small fishing prams etc. Typically they have much longer waterlines etc.

With all engine/dingy combos it is the pair that much work together. The purpose of the account was to reinforce that as a fairly minor change in pitch had a significant change in performance. A smaller pitch allows less initial load on the engine so it 'spins up' faster allowing for more HP to be delivered. An increased pitch has more bite with each revolution produces more thrust but the engine works harder. If the boat planes very easily then the increased pitch will give a higher top end, conversely if the boat does not get up on plane easily the engine is overproped for the boat and decreasing pitch has the effect shown.

Net is that the boat planes easier but I sacrificed a little bit of top end speed.

[Raven]

I'm running a 6hp Yamaha 2 cylinder four stroke on my 9'6" Zodiac. I've often wondered if it might be worthwhile to fine tune the prop to that boat/motor/typical load, but I haven't found a good source for aftermarket props for that small of an engine. Is it perhaps not worthwhile to experiment with props on an 80 lb boat with a 6hp motor? If it is, do any of you know of a place that has a selection of props to fit my motor?

[wind rose ll]

Jon;
l have the same Caribe and Yamaha and the same problem .
What is the diameter and pitch of your new prop?.
Dave

[Jon D]

Originally Posted by wind rose ll

Jon;
l have the same Caribe and Yamaha and the same problem .
What is the diameter and pitch of your new prop?.
Dave

Dave

I think I went to a 9 1/4 by 9 which should be about 1" less pitch than what you have on there now.

[wind rose ll]

Jon;
l just installed the 91/4 x 9" prop on my Yamaha 15hp and find it is making a ringing type noise that a friend believes may be cavitation prop noise. Have you experienced this when you changed prop pitch?
Dave

[Jon D]

Originally Posted by wind rose ll

Jon;
l just installed the 91/4 x 9" prop on my Yamaha 15hp and find it is making a ringing type noise that a friend believes may be cavitation prop noise. Have you experienced this when you changed prop pitch?
Dave

Dave

just happened to be on line..it has a different noise than before but nothing I would describe as a ringing... if it is cavitation then the noise should vary with throttle. i tend only to use full or almost full throttle to get on plane then quickly can throttle way back to keep it up on plane. at those speeds no unusual noises.

[wind rose ll]

Ya no noise at planing speeds but at low to mid range l am getting this noise..may not be a ringing but was NOT there with the old prop,l wrote to Michigan Wheel (the manufacturer) to see if they could shed some light on the issue.....Thanks for the rapid response
Dave