Prop query for the experts - I'm not.

[umblecumbuz]

We have a workboat - Dauntless 13 1996, with a Johnson twin 50hp 96. The prop is a Michigan 11.5 by 19 pitch.<br /><br />With helmsman, twelve gallons fuel and about 50/60lbs of gear, she runs 5700 wot. With three up and more gear, she still runs just over 5400 wot. We tend to run wot constantly, sea state permitting. We have autotabs, similar to Smart Tabs in operation, and these have made a huge difference.<br /><br />We feel the need to go up a pitch, but several firms we've approached seem useless with advice, and one has stupidly said that you can't get a 11.5 with a pitch greater than 19 (I think he was confused, because Michigan only run to 19 for this aluminum series.)<br /><br />So we need advice as to what prop to buy. If it produces extra top end, that's to our advantage. Time is money!

 

[Dhadley]

Re: Prop query for the experts - I'm not.

I wouldnt go with any higher pitch. Youre barely in the right rpm range now with one person. Actually if it were up to me I'd look at the set up to try and gain more rpm with that prop.

 

[Laddies]

Re: Prop query for the experts - I'm not.

You might consider haveing your props double cupped, that should increase speed and hold in better in rough sea---Bob

 

[Dhadley]

Re: Prop query for the experts - I'm not.

Adding cupping will pull the rpm down and its barely turning enough now.

 

[pwiseman]

Re: Prop query for the experts - I'm not.

Originally posted by stillfishing:<br /> We have a workboat - Dauntless 13 1996, with a Johnson twin 50hp 96. The prop is a Michigan 11.5 by 19 pitch.<br /><br />With helmsman, twelve gallons fuel and about 50/60lbs of gear, she runs 5700 wot. With three up and more gear, she still runs just over 5400 wot. We tend to run wot constantly, sea state permitting. We have autotabs, similar to Smart Tabs in operation, and these have made a huge difference.<br /><br /><br />We feel the need to go up a pitch, but several firms we've approached seem useless with advice, and one has stupidly said that you can't get a 11.5 with a pitch greater than 19 (I think he was confused, because Michigan only run to 19 for this aluminum series.)<br /><br />So we need advice as to what prop to buy. If it produces extra top end, that's to our advantage. Time is money!

You are real close to optimal with light load and borderline overproped with a heavy load. Going up would likely result in further loss of RPM becuase your motor does not have the mojo it needs to keep the RPMs up where you want them. Going down might get you 200 extra RPM, but you will probably not increase in speed at all with the lower pitch. I would try to eek out a little more by reducing the resistance on your current prop so the motor can turn it faster. Would not take much tweeking. One way to do that would be reducing the diameter a tiny bit.

 

[moderator1]

Re: Prop query for the experts - I'm not.

Reducing diameter is reducing efficiency...Raising the engine on the transom would be the best option to start with..<br />5800 with a load would be the perfect target.

 

[umblecumbuz]

Re: Prop query for the experts - I'm not.

Thanks for the input fella's.<br /><br />We must be mistaken! Our engine manual (I won't say the name, but it begins with Cly...) tells us that wot on this motor is 5,500. Hence the interest in reducing our regular 5700 wot.<br /><br />Dhadley - what is wot on this motor? It's obviously more than we're getting, so we need to do work on the prop setup. Is there a recommendation from you for a replacement prop? We would stick with aluminum because we tend to clout the prop fairly frequently. Ours is already a bit dinged.<br /><br />Thanks.

 

[moderator1]

Re: Prop query for the experts - I'm not.

Your engine was built to run on fuel of a much better quality in 1996 than what we have today.<br />We've found longer engine life and better performance on todays fuel in these engines when run a bit higher on RPM.<br />Obviously you would like Dhadley's opinion on this, so let's see what he has to say.....

 

[TwoBallScrewBall]

Re: Prop query for the experts - I'm not.

I'll bet you a donut he says 6000R.