1997 mariner 60hp bigfoot rpm and prop questions

[trent0416]

hello all. i have a 1997 60hp 2 stroke bigfoot on my 20 foot pontoon, and a main issue is the rpm gauge does not work, thus not allowing me to monitor proper rpm, but this boat is a dog loaded or empty. first i need information on where my proper rpms should be for this motor, and is there any specific recommendation for prop diameter and pitch as well? i know this boat will not be fast by any means, but i just want it at max performance for what i have. i am lucky to get 10-12 mph out of this thing and it makes me wonder if my prop is too big for this. it currently has a 12 pitch, and once i get my gauge corrected i have a feeling my rpms are gonna be very low. also will there be any benefit by investing in a hydro-foil? any information here would be much appreciated. thanks.

Trent

 

[The Rooster]

Re: 1997 mariner 60hp bigfoot rpm and prop questions

Trent, those older 2-stroke 60 hp's should run at 5500 rpm's max. Shoot for that when you confirm w/ your tach. Might take a 10 or 11 pitch prop. You should be running a good bit faster w/ that combo. Maybe 17-18 mph. I wouldn't waste money on a hydrofoil. Hopefully others w/ similar combo's will chime in soon. If not, you might post in the Merc. engine forum. Good luck !!!

 

[steelespike]

Re: 1997 mariner 60hp bigfoot rpm and prop questions

Do you know thw gear ratio of your big foot?
I'm guessing 2.23.?

 

[trent0416]

Re: 1997 mariner 60hp bigfoot rpm and prop questions

thank you for the info. i have read several other forums that are saying a 20 foot with a 60 hp bigfoot should have a 9 pitch prop for best performance, do you think that will push me over my 5500 limit? also do you think there is anything else i should be checking, or just get my tach and prop corrected and go from there?

also im sorry, but i do not know the gear ratio off hand, but what you described sounds familiar when i ordered new water pump impeller last year. any additional info would be great! i sure appreciate it

Trent

 

[steelespike]

Re: 1997 mariner 60hp bigfoot rpm and prop questions

After a little research it appears the gear ratio is 2.31.
Pontoon tests speeds and prop results are all over the place for no apparent reason.
Using some Merc 4 st.60 bigfoot tests,2.33,ratio Typical prop was 11" with a low of 10 and a high of 13.
Speeds from 18 to 22.6, rpm from 5600-6000.The 4 stroke can run up to 6000 so if it can turn the prop that fast
its 500 higher than the Mariner.Thus assuming the same prop; faster.
It does appear that a healthy Mariner 60 could run 18 to 22 mph.It also appears your prop is in the ball park
Some things to check; Compression,does the throttle open all the way,is the motor in excellent tune?
Eliminate any excess weight,distribute the weight for the best speed,are the tubes smooth and clean?
get the rpm and gps speed we should be able to tell what is needed.

 

[trent0416]

Re: 1997 mariner 60hp bigfoot rpm and prop questions

thanks. replaced the gauges today, getting a signal from tach when trying to turn it over, so hopefully that is working now, but the river is currently flooded so may be a bit yet before i can confirm wot rpm's. with that, i read that the motor position can cause issues as well. im hearing that the motor cavatation plate should be level with bottom of transom for best performance. is this the case? mine appears to be roughly 2-3 inches lower. any info would be great. thanks

 

[steelespike]

Re: 1997 mariner 60hp bigfoot rpm and prop questions

If your not getting any ventilation (cavitation) the motor might be too low.But don't expect much change unless your really dragging a lot of motor. Get some tests with rpm and gps speed when the water clears

 

[phillnjack2]

Re: 1997 mariner 60hp bigfoot rpm and prop questions

with a smaller gearcase 60 and a 12 inch pitch those engines reach 5500 on speedboats
i would say you are way overpitched and i would go straight for a max of 10 inch.
if after a while it reaches max revs but poor hole shot, then drill the prop hub with 1/4 holes.
if anyone says this dont work they dont know what they are talking about, it realy does work and especially on heavy boats.

here is a pic of what i mean by drilling it, its exactly the same as the big expensive merc vented props.
the exhaust escapes and helps to let the prop spin upto the revs and the boat gets going quicker.
once up and running about 2500 to 3000 its like no holes are in the prop.
but on pull away its like dropping a couple of inches.

phot to show what i mean and what i done to mine.
some stainless props come like this already drilled, but i have found it to be just as good on alloy props.
it will not harm the prop in any way, and you can always just put a plastic plug in the hole if you dont like it.
i have found i could use a 14 pitch prop when drilled for top speed and good holeshot, but only a 12 pitch without the holes ??
it realy does work.
Just make sure the prop can reach the correct revs before you drill for holeshot.
you want to see top end of 5500rpms. and i reckon about 18 mph on a 20 foot pontoon boat with just a 60hp