Help With Propping A 35hp merc

[Carsen]

I haven't been on the forum for a really long time, but since spring is almost coming around I'd like to figure out what I'm going to do for propping.

I've got a wooden Glen-L TNT (12ft) with a 35hp 1971 Merc shortshaft. Currently, i just have a stock 3 blade and a 2 blade, both which were awful last season. The 3-blade runs ok, but I know I can get a ton more speed with the right prop.

I obviously don't have knowledge on prop selection, but I do know a bit about props. Any input would be great, and if you need any more info to make a suggestion just ask. Thanks.

[Dhadley]

Is the 3 blade in the ballpark as far as rpm? What's the pitch? I have a bunch of those small props and can probably get you what you need but we need a starting point.

[150aintenuff]

welcome to the club... you arent the only one with an older engine with prop issues.... ive been looking for a year. and no luck only one I found was equal to a 3 or 4 out of 10 on the S&F scale and the local prop shop wont work it over to make it right so i have a great boat anchor... (found at a local salvage yard... dont want to have anyone think that i got it from here)

[at100plus]

I don't think you can pop a merc they are patented and Brunswick has the molds. ;)

[Carsen]

Is the 3 blade in the ballpark as far as rpm? What's the pitch? I have a bunch of those small props and can probably get you what you need but we need a starting point.

i'd say the 3 blade runs decent rpm, but i dont have a tach. the diameter is 10" and im not sure of the pitch. all the prop says on it is " 2118 " near the base of one of the blades, and " SS " on the body of prop.

is there any way to measure the pitch? im sure 2118 can tell something about the prop.

i was just looking for a mini chopper, but i wouldn't mind trying a cleaver either.

however, i want to make as best of a choice i can make in the first place.

[David]

Merc used to make an 10.375" X 18" chopper for the 25 HP
That would be a good place to start, but you might have to re-hub.

Maybe you can find a Merc Voo Doo/Critchfield/Delta racer and see if any of their props fit.

You should buy a tach and borrow a gps.

You can borrow my props and gps if you can visit me in Orillia. I have the 18" chopper and another 20" prop. Neither is for sale. Racers or ex racers may have old props for sale.

[JLeus]

Not much "portable hop ups" here but alot of good info has been applied for me. Not hi-jacking but..... if you are in the upper reaches of the operational range (TinyTach present, great product) is there some speed to be found in prop style changes. I have a good prop shop that lets me use his tools to measure my self made changes which is basically additional cup. The prop bites well and pulls out of the hole good but I wonder if a steeper pitched prop would run faster than my cupped prop. I would expect to loose some hole shot but would less cup/greater pitch run faster? I am limited by fit in as much as I am working with a Suzuki 25 (with added T&T, back about 6", anti-ventilation plate above water when WOT) and from what I understand few other thru hub applications will work with out interference with the lowers case. The exhaust is relieved at the lower....would working on finding an over the hub give me any advantage? I can see overcoming some of the clearance issues with the carrier when using a small hubbed prop. Any input is appreciated and no guarantees are expected. Thanks, Jim.

[Carsen]

Merc used to make an 10.375" X 18" chopper for the 25 HP
That would be a good place to start, but you might have to re-hub.

Maybe you can find a Merc Voo Doo/Critchfield/Delta racer and see if any of their props fit.

You should buy a tach and borrow a gps.

You can borrow my props and gps if you can visit me in Orillia. I have the 18" chopper and another 20" prop. Neither is for sale. Racers or ex racers may have old props for sale.


yeah i have a cottage near wasaga, so thats an option, thanks for the offer.

[David]

Of course we don't know if my hubs will fit your shafts

I know my props will fit a 1976 Merc 65. My 76 brochure shows the same range of pitches for the 40 and the 65. I think the 40 is more or less the same as your 35. So maybe you are in luck.

shoot me a PM or e mail and I can send you my home and cottage phone numbers

[150aintenuff]

the 35 uses the same 13 spline props as the 40,50,60,70 hp used in the 70's -current. the 25Hp splines are different and will not work so at minimum a rehub would be required for overhub props.. through hubs no chance of fitting.

[David]

Since your 35 uses the same hubs as the '40,50,60,70 hp used in the 70's ' then my props will fit. My 18" chopper had already been re-hubbed and my 20" dumbo is correct. Visit me, and you can try them.

Check out the thread on Canadian formula V racing. Maybe one of the Merc guys will sell you a prop.