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-   -   the correct prop. (http://www.sailnet.com/forums/gear-maintenance/42459-correct-prop.html)

exfus55 04-21-2008 08:28 PM

the correct prop.
 
My wife and I just got into Tacoma today on our new (to us) newport 28 mkII . We left Bellingham sat. at noon in a snow storm. We love the boat ,pretty much everything works,(it is a 1983 boat) My one area of concern is speed under power.We spent the whole trip powering, 20 hours total, as there was no, or very light winds.The boat has a 11 hp universal diesel turning a 12x12 2 blade prop. My question is should I be able to get more than 5 kts. from it on flat water? Anyone have any thoughts on this? thanks

Faster 04-21-2008 08:44 PM

Have you had a recent haulout/clean? That can make a big difference if the hull and prop are not clean.

What rpm are you running at? If the engine starts pushing black smoke when you try get max rpm, it (the prop) may be too "square" and a re-pitch to 12x10 or 11 may work better for you.

Presumably this set up has been satisfactory in the past....

Rockter 04-21-2008 10:10 PM

Yes, surface finish below waterline is vital. I once calibrated my 36 ft ship with fine weed on the hull, and it pulled 5.5 kt at 1750 rpm, in flat calm.
Next day, with the weed scraped off, at the same revs it pulled 6.6 kt !!

MedSailor 04-21-2008 10:50 PM

Congratulations on your new purchase! I also bought my boat in Bellingham (From Bill at Bellhaven Yacht sales) and I also am wondering about my prop....

You could definitely have fouling on the hull or the prop. A neighbor of mine, with a newport, had barnacles on this prop and could only do 2.7kts. He cleaned off the prop, but not the hull and was up past 6kts.

Michigan wheel has a long detailed online form that will tell you what size/pitch prop you should have. You could fill that out and see what they say. You should also look at your engine manual and see what rated your rated RPM is and if you are getting to 80% of that or not.

If you're not getting to rated RPM you could have a throttle linkage problem, fuel starvation problem, mis-sized prop, underwater fouling, old/bad fuel..... etc.

Enjoy your new boat!

MedSailor

artbyjody 04-21-2008 11:26 PM

That particular boat will only get maybe 5.9 - 6.0 knots. Just because the water was calm on the surface didn't mean that you were running against a ebbing tide. Other factors include how heavily the boat was loaded with gear and weight of all persons. My C-27 when not loaded and just me could pull almost 6 knots, but loaded down with gear (BBQs and stocked fridge, and other comforts) 5 knots was the norm and on a good day 5.2 (hull was clean).

So many other factors to consider, congrats as well.

Rockter 04-22-2008 07:44 AM

But if you are running against a tide you will still have the same water speed on the water speed indicator.

JimsCAL 04-22-2008 08:57 AM

I have a 5411 in my Cal 9.2. It only displaces 7000 lbs. Prop is a 14 inch diameter by 10 inch pitch folder. This combination seems to work fine. I agree with Faster that the pitch may be too high, and if a slightly larger diameter prop will fit (with adequate clearance) that might also help.

roline 05-23-2009 04:48 PM

The 9.2's original universal diesel was repalced with an Yanmar 2GM20 (16hp) with a Martec 14D12P folding prop. 6.4 knots at 2900RPM with is close enough to hull speed to be the most efficient spot. More RPM just burns lots more fuel.
The graph is located AT:
http://www.angelfire.com/tn/santana525/cal92/SPEED.JPG


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