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Prop questions 1996 75hp Mariner

C

cakayaq

New member
"I'm in the market for a n

"I'm in the market for a new prop. I'm currently running a 4 blade 12.75 x 17 Solas, my boat came with (I bought it used) a 3 blade 13 x 19 Quicksilver. Right now, I can't quote my actual WOT rpm but I'm going to take it out to the river tonight and get it, but my feeling is that I can go over the WOT by about 400 rpms. My Mariner manual says the full throttle range is 4750 - 5250. I'm fairly sure I can hit 5500 if I try and maybe a little more.

One more thing. I measured from the shaft to the bottom of the plate and it is 7.5 inches.

So here are the questions.

**Should I go with the largest diameter prop I can use and then adjust the pitch to get into upper end of the WOT range?

**Or should I go with a smaller diameter and get a larger pitch. to bring down the rpms and get into the range?

FYI, I'm a river boater, and often it's in swift water with a ravel bottom with the motor lifted as high as I can. I'm leaning to the largest diameter prop so I can keep as much prop in the water as I can when I lift it.

I'm trying to hone in on the best prop in aluminum before I buy a stainless

**What do you think would be the maximum diameter? The manual does not say. How much clearance do I need?"
 
"You should be shooting for 50

"You should be shooting for 5000 rpms bang on with that particular model (Optimum WOT is max minus 200, give or take 50 rpms) - so if you can hit 5500 you have "too small" of a prop.

The diameter of a prop will also affect the rpms - more diameter = more surface pushing on the water = less rpms, just not to the same extent as the pitch affects it.

If your running the 4 blade (with the specs you list), it sounds like the 3 blade 13 x 19 should be about bang on (2 extra inches of pitch = -400 rpms, going from 4 to 3 blades, +50 or so, but a bit more diameter, so that's a wash).

If there is nothing wrong with your 13x19 I would use that one. If you are partial to Solas (and I love them personally), you could run a 13X19 Amita 3 (super quality aluminum).

In the pitches you would need on that, most props will not have a diameter significantly greater than 13", so you don't have alot of choice/wiggle room in that regard unless you are looking at some custom work..."
 
"Graham thanks for the help.

"Graham thanks for the help.

I did take it out last night and I hit 5600 with the boat trimed out, and the transom jack almost all the way up. With the transom jack down where I usually run it was more like 5500. That was with 550lb of passenger and another 200 of supplies and a fullish tank of fuel so I'd say weight wise it was a good average load.

The 13x19 would have been perfect except that I chewed it up on a gravel bar last week. It was my "rock prop" but now it looks more like a fancy anchor.
That's why I'm in the market for a new one.

Am I right in thinking that the difference between a 4 blade and a 3 blade is about 50 rpm?"
 
"A 4 blade (all else being

"A 4 blade (all else being equal) will usually make a difference of about 50 rpms or so. Your Solas is slightly cupped and the cupping will cut off another 50 (100 total).

You could grab another 4 blade at 19 pitch (or even a 21 - you won't find a 20 pitch) and keep your current one for those times that you take a "boatload" out with you.

It's always advisable to have 2 different props for changing circumstances and the 4 blades really do let you stay on plane at a lower speed than a 3, get you there faster, and actually vibrate a whole lot less which is always a good thing, especially for the lower unit.

The trade off is about 2 or 3 mph at top end...."
 
"Sorry, what I was going to me

"Sorry, what I was going to mention, if you are after another Solas and are looking for a great deal you can check out www.a1discountprop.com/solasmercmaralcup.htm

I deal with these guys and have had zero issues.

You can get an Alcup D3 or D4 for your motor for under 90 bucks, and that includes the hub kit (these have the removable/replaceable hubs - nice). I run the 4 blade Alcup's in canals and just love em.

Or if you just hit their main website, they carry a great selection, prices are great and they will UPS it to you in a day or so...."
 
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