Prairie 29 engines

Baker,
I think he's so overpropped WOT would'nt produce enough power for the comparison you're looking for. He'd need to get propped right to make enough engine speed to make enough power to plane the Prairie. And depending on prop clearence there may not be enough room for a suitable prop. He gets his cruising speed at less than half the rpm I run .. propped to 3000rpm.

I went back to post #78 and if the lower pic is a Prairie it should plane and a 6-354 should be enough power to do it .... if propped to rated rpm. However the round chines and too much weight aft likely could prevent planing. Too much angle of attack and even a hull that normally planes may not.

Baker:

The engine tops out at about 2,100 rpm, and the black smoke indicates it's definitely overloaded and overfueling. Clearly I don't run 'er at that more than momentarily. The boat doesn't even come close to planing.

The P.O. even put trim tabs on 'er to try to get the stern out of the hole - doesn't do any good.

The engine is a "Range-4", rated 185 BHP @ 2,400 rpm, according to the manual. It weighs 1,400 lb with a Borg-Warner gear on 'er, so there's an extra 6-800 lbs in the boat that ain't helping things. The governor does hold 'er to 2500 when it's out of gear, so the governor setting isn't holding it back.

Paperwork on the boat says it was built with a 4-154, so it was repowered at some point - I wish he'd stuck with around 80 HP, which would be more economical. OTOH, this huge engine makes it possible to be this drastically over-propped which means I can cruise at engine speeds that sound like a fast idle, which is very nice.

With what I paid for her, I can afford to repower at some point - whenever the mood strikes me, or when I get a chance to buy a suitable engine. The last boat I had (an Albin 25) I repowered with an industrial engine which was built for a generator or a forklift or something like that. If I get a shot at an 80 HP Kubota, Isuzu, Yanmar or Mitsubishi, there's no telling what I might do...

Onward!


JS

John,
Good to hear from you and the current results. The subject always elicits opposing opinions regarding propping and always will. I too as mentioned in the past, am way over propped. Max RPM 2000 from a two levels of factory rating RPM 2500 or 2800. Which ever, like you at 1400 RPM with a cushion of 600 RPM or 3/4 throttle used, achieve the hull speed of our 27 foot SD hull of 6.9 to 7.3 knots, burning 1.5 gallon per hour.

From another thread regarding 'sound of your engine' where decibels were discussed, the thought of obtaining a decibel meter was broached and I downloaded a inexpensive app called 'logSPL Cost $1.99.
At 1400 RPM the cabin level is 71.3 decibels. On the fly bridge it is 60.1 dBs
According to the comments on that thread, my sound level is good and normal if not low.

Like you, the comfort, the sound, the achievement of hull speed plus equates to having a satisfactory situation all other things being equal.

Al-27 foot Marben pocket CRUISER

I am taking prop off boat this week and taking it (and the spare) to Scandia Propellor in Fairhaven.

Inspection and to have them tell me what the specs actually are for both props.

I am concerned about 'dezincification'. PO had been slathering bottom paint on the prop. Hopefully they are OK.

Are you really concerned that the manufacturers of marine propellers are not aware of the selective corrosion of zinc from brass, and don't take care to use the correct corrosion resistant alloys?

I had always assumed they were properly informed about the issue and were on top of it.

I would be interested, indeed if it turns out you have an issue.

My underwater gear looks fine to the naked eye, with no signs of the telltale red corrosion products. While I have no idea, nor interest in the specs of the propeller, rudder and so on, the potential for corrosion is at least a little alarming.

Thanks

JS

The manufacturers are aware. But apparently the PO was not aware of the undesirability to slather copper ablative bottom paint on the props.

The copper draws out the Zinc, severely weakening the prop. To be honest, I am not sure if the props I have are straight Bronze or Nibral (doubt it). But the prop shop would know. Apparently straight bronze is the most susceptible to dezincification issues.

I just want to clean up and inspect to see what is there. Hoping I don't have to buy a new prop.

That's sort of my issue. I can't tell if the props are dezinced or not, Since there covered in paint. I sanded them a bit. But it all looks the same color. Not really pink, But I don't know enough to know....

I have never had 'no zincs' in the two years I've owned her. So hopefully it's a non issue.

Repropping Results

Sorry for the tardy follow-up.

Willow-B had a 18X12 3-blade prop that was re-pitched to 18X14... Which means that I am out of luck with adding any more pitch to this prop.

So I added a moderate cup to this prop. Per the Prop Shop it will make the prop more aggressive, which translates to moving more water. AND at a price of $25/blade. Can't beat the price!

The Result:
This dropped my WOT from 3200 to 3000 and dropped my cruise setting (75%) from 2400 to 2200. My cruise performance went from 5.8k to 6.2k with a 200 drop in rpms. Good enough...

So far the only difference I've experienced is a bit less starboard prop walk while backing. I used this prop walk to my advantage while docking.

Nomad Willy said:

Baker,
I think he's so overpropped WOT would'nt produce enough power for the comparison you're looking for. He'd need to get propped right to make enough engine speed to make enough power to plane the Prairie. And depending on prop clearence there may not be enough room for a suitable prop. He gets his cruising speed at less than half the rpm I run .. propped to 3000rpm.

I went back to post #78 and if the lower pic is a Prairie it should plane and a 6-354 should be enough power to do it .... if propped to rated rpm. However the round chines and too much weight aft likely could prevent planing. Too much angle of attack and even a hull that normally planes may not.

Click to expand...

You can forget planning a prairie 29-no matter what engine and prop is in it. I think it would take about 400 hp to come close-but would probably just dig a deeper hole:lol:

ddalme said:

You can forget planning a prairie 29-no matter what engine and prop is in it. I think it would take about 400 hp to come close-but would probably just dig a deeper hole:lol:

Click to expand...

The only plaining I can do on my Prairie is explaining to my wife why I need to spend more $$$$$. That's all the 'splaining I got to do Lucy.

ddalme,
Agree,
But note I did'nt say plane gracefully.
And I was'nt thinking 20 knots.
But 400hp should get well above disp speed and the transom exposed to air (planing).