Prop Advice

[RubTJicon]

My brother and I have took on a new type a project, far away from our normal Jeep stuff.

We started working on a boat. It has a 1970 model Merc 1100ss on it. I'm looking for advice on choosing a new propeller as the one that is on it, is aluminum, and pretty banged up. It is a 16' bass boat if it makes a difference.

On our maiden test voyage yesterday, we did manage to get 30.8 mph out of it, with 4 adults on it.

Is there anything to be gained by going to a 4 blade vs the 3 blade ? The tach hand isn't working, as the motor is on an '82 model boat, so I cant tell you what RPM range we were in.

Please excuse my ignorance on this subject, but I am a newbie to anything marine.

Thanks guys

 

[Bob_VT]

Re: Prop Advice

Welcome to iboats.

Prop depends on the use. If you are always (normally) going to have 4 adults a neww prop of 3 or 4 blade will work.

Check out the iboats prop selection...... if you stay with a 3 blade aluminum it will be the cheapest and best bang for the buck http://boatpropellers.iboats.com/?*******=666745524&**********=579093965

Be sure to match the pitch of what you have now. Do you have a tach? That motor should be running 5500-5800 RPMS when wide open.

 

[RubTJicon]

Re: Prop Advice

It has a tach but it isn't working. I guess whoever swapped motors never hooked it up.

 

[steelespike]

Re: Prop Advice

Welcome,I'll try to get you started.If you read the stickies at the top of the page
and the helps at the prop store page it will help you understand prop selection a little better and of course any confusion be sure to ask any questions that occur to you.Your motor needs to operate near the top of it rpm rating at wot(wide open throttle) this is occomplished with the setup and prop selection.Basically higher pitch(higher number) reduces rpm
lower pitch increases rpm.Prop selection is like trying to pick a single gear in a car to do everything.
First I believe your motor is a 66 or 67. It may have battery or Thunderbolt ignition.Timing is critical and you should definately work with a manual.Johns Old Mercury Web Site may be a good source of info and parts.A prop shop may be able to repair the prop.Then you can get some accurate perfornance numbers.
We really will need your max rpm and speed and the size of your prop.(usually on
the barrel or under the prop nut)
We need the size,type and dry weight of the boat.Aluminum or fiberglass?The antiventplate,just above the prop should be visable at speed.Usually ends up about an inch higher than the bottom.Does the boat respond when you trim the motor out(prop away from the boat)?You may be able to get a Tinytach for your motor.About $47 and easy to install.They work by induction from a plug wire.If its battery ignition a regular tach should work.

 

[RubTJicon]

Re: Prop Advice

The motor does say Thunderbolt Ignition on it. It is a 16 foot fiberglass boat, weigh I have no idea though.


Edit: It is a 16' , 1982 Mastercraft Cajun if that helps.

 

[RubTJicon]

Re: Prop Advice

Anyone know the weight of the Cajun ?