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Author Topic:   Props for smaller engines
jimh posted 04-01-2000 11:39 AM ET (US)   Profile for jimh   Send Email to jimh  
There seems to be a huge selection of props for larger engines, 70 HP and up, but when I look for propeller options for my old Merc 50HP, I don't see nearly as many.

Mostly there are 3-blade aluminum props with pitch variations from about 12 to 17 inches. They are all about the same diameter, 10.125.

Anyone have any experience with other props for this size engine?

The problem for me with the current set up is that right at the RPM/Speed where the boat comes on plane, the engine seems to be laboring like it doesn't have the power/torque needed. So it is very hard to hold the boat on that slow plane setting.

Intuitively, it seems like moving to a prop with less pitch and more diameter might give me more "bite" and move the engine RPM up a little to where the engine has sufficient power to hold the boat on plane at the lower speed.

Maybe the throttle setting is right at the point of opening up the carburetor secondaries. This would account for the touchiness of the setting.

Comments welcomed!

--jim

lhg posted 04-01-2000 02:19 PM ET (US)     Profile for lhg    
Jim: You have mentioned this problem elsewhere on the Forum, and I think
Clark Roberts recommended you drop down to a 14" pitch prop. I'd agree with his recommendation if max top speed is not your primary concern, although I actually don't think you'll lose that much. Regarding availability of props, you have three choices.
1. The Merc alum models you have mentioned. These are the bottom line in performance & cost, but in your case may be all that you need.

2. Mercury Vengeance SS props. Still of conventional "elephant ear" design, but definitely superior in holding and efficiency over aluminium, and may help solve your problem, if indeed it can be solved.
(putting weight forward can also help your boat plane slower) Mercury believes that the higher rake, progressive pitch props do not mean much under 40mph, so that is why they do not have other higher performance offerings for the small gear case.

3. There are some after market props made in the performance SS style that you might want to consider. I think if I had your rig, this is what I'd do, although I have no first hand experience with these props on small boats.
My first choice would be Michigan Wheel's "Rapture" line, about $225 at Cabela's, and probably a special order. They are also shown in the West Marine catalog for more money. This is a performance prop and it is made to fit your engine. Stiletto props also make a model for your engine, called a "Triad II", available from Overton's for $214. Either one of these should give you higher top speed and more bow lift for fuel efficiency.

Buying props for a boat is always a chance and a guess. I'd hate to tell you how much I've wasted on the wrong props over the years!

Clark Roberts posted 04-01-2000 04:34 PM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Jim, dropping down to a lower pitch should give you the holding power you seem to need.. an inch should do it and I agree with Larry that you won't loose much top end, if any! The style of prop can cause the "touchyness" you descripe and tendency to drop off plane, constant fiddling... etc!
A "high rake" prop wastes lots of energy trying to lift the bow and is effective only
on hulls that run almost free of the water, like bass boats.. a lot of water comes off the tips of the prop in a radial fashion and don't contribute to forward motion.. a std. prop design (double cupped blades) sends the water off the tip and trailing edge of the prop straight back and don't waste energy spinning water radially!! At least that's the best way I can describe it.. I have had good luck running a 14" pitch Yamaha prop on 40 and 50 hp Mercs... it has a "cleaver" style to the blades, which are very thin and a real "meaty" cup area.. the Yam props will slip right on but you have to get a big washer to put under the prop nut... Good luck... Happy Whalin'.. clark
jimh posted 04-01-2000 10:26 PM ET (US)     Profile for jimh  Send Email to jimh     
Deja Vu...

You know what, I had my settings for the forum in the "default" SHOW LAST 20 DAYS mode and I didn't see that we'd discussed this last month. I guess I am getting senile in my old age (49).

Well, thanks again for pointing me in the right direction, and I should mention that it might be a good idea to widen the range of dates for your forum articles when researching! As I just learned !

--jim

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