mercury prop problem

[razorsfishing]

Hi.I have a problem that mabe a member can help with.Doe,s anyone know the size and part number for a mercury 75 15 degree pitch prop.I have changed from a 19 pitch to a 17 and the engine runs at 3500 revs at top speed.I have been told that to increase speed and revs i need a 15 degree pitch prop.Has anyone got the info to help.I woululd be pleased to have a chat and can be contacted on 01323 873033 or if a num is available will phone.Or if anyone in the forum can tell me where to go for this item i would be grateful .Cheers chris

[Charter Skipper]

You could try contacting your nearest Mercury dealer....i think you`ll find them listed on the Mercury main site

http://www.mercurymarine.com/

[Muzzer]

Hi,

in general, most props are marked with a numbers, such as "13.75x21". the first number refers to the prop's diameter, which is defined as twice the distance from the center of the hub to the outer edge of the blade. (measured in inches). The second number designates the pitch, or the distance the prop will move the boat forward with each revolution. In this example, the blades will draw a 13.75 inch diameter circle and the prop will move the boat forward 21 inches each time it goes around.
In reality, the prop won't move the boat forward 21 inches per revolution; the actual distance will be somewhat less and the difference is called prop slip. This is not a bad thing, because a prop must slip to develop thrust. Prop slip can be as little as 8 percent for fast, lightweight hulls, and as much as 20 percent for heavier boats.
Engine manufacturers specify a maximum wide-open-throttle (WOT) rpm limit, or more often, a WOT rpm range. The objective is to select a prop that allows the engine to rev to this limit or into this range when operating at WOT while the boat is carrying a typical load. Pitch is the measurement that most closely controls WOT rpm.
As a general rule and depending on gear ratio, we can expect engine speed to go up by 100 to 200 rpm for each 1-inch reduction in pitch. Conversely, for every 1-inch increase, engine speed will fall by 100 to 200 rpm. Keep in mind that engine is not the same as boat speed.

To throw a further spanner in the works - it may be better if you can find a "variable pitch" prop. It is also worth remembering that if you can get hold of a four bladed prop, then you will need to reduce the pitch by one degree.

[razorsfishing]

thank you for the info

[Lookfar]

I'm running an Evinrude 75 on a 16.5ft planing hull and the 17" prop issued with that was too large. Dropping to 15" sorted it nicely, jumping peak revs from 4400 to 5200rpm. I didn't get an Evinrude prop though, a mate picked up a suitable Solas prop for me from a chandlers on the South Coast. I'd suggest you look on the internet then ring around a bit, might save a few pennies compared with going through the nearest dealer?

Steve

[keana]

Originally Posted by Lookfar

I'm running an Evinrude 75 on a 16.5ft planing hull and the 17" prop issued with that was too large. Dropping to 15" sorted it nicely, jumping peak revs from 4400 to 5200rpm. I didn't get an Evinrude prop though, a mate picked up a suitable Solas prop for me from a chandlers on the South Coast. I'd suggest you look on the internet then ring around a bit, might save a few pennies compared with going through the nearest dealer?

Steve

Is that the E Tec your running Steve? If so how do you find it?

[Lookfar]

Originally Posted by keana

Is that the E Tec your running Steve? If so how do you find it?

I just go to the back of the boat and it's there

Seriously, it has given me no grief yet. The old Mariner Bigfoot I had was a typical 2 stroke, went like stink but had starting issues from very cold or very hot. The etec just fires first turn of the key and runs. Very crisp pick-up out of the hole, where some of the 4 stroke-powered 165's are more progressive. Throttle response if anything is too sharp, it is very easy to give it too much when you are diddling around in harbour at close quarters. Only time it has struggled was once setting off in sub-zero temperatures. I have the low temperature oil in it but it still alarmed and shut down to tick-over for a few minutes just after setting off. Ray's etec was doing the same thing and we were both smoking like stink so the over-oil function must have kicked in.
Early etecs had a good 17" prop, with a racy leaf-like blade profile. That prop on a 165 puts you half into the recommended rev range at WOT. Perfect. The later 17" prop does not even reach the recommended range. Warrior advise that you will get better economy that way (it still pulls 28 knots+) but the usual advice is that it will result in excessive drivetrain wear. If you see a broad-bladed 17" prop with the rig then start asking questions about max rpm because a replacement 15" will be about £100.
If you go for a 4 stroke, be aware that some of them foul the transom on full tilt. Not a problem when running along but could be costly if you forgot when tipping the engine up.

Steve

[priji]

You could try contacting your nearest Mercury dealer

[Codfather]

Here are a couple of sites that might help

http://www.clementsmarine.co.uk/proprevs.asp

or

http://www.steeldevelopments.co.uk/

Coddy