reproping a pontoon

MH Hawker

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1988 Riviera Cruiser
length 20 feet
dry weight 1050 lbs
motor weight 130 lbs
beer n gear n gas 300 lbs
total 1480

1988 nissian NS40
40 HP two stroke
LU gear ratio 13:25
prop alu 3 blade 11 p 10.6 x 12.7

netural rpm= 1000
idle rpm= 850
WOT rpm= 5200-5800

test results
using a clamp on inductive tach + or -1 %
boat WOT=4275
boat speed GPS= 14 mpg


going by the 300 to 400 rule changing to
a 9 p would put it in the 4600 range
a 7 p would put it in the 5000 range
a 5 p would put it in the 5300 range

I would like to get it closer to the 5200 or 5400 opperating range and being as i often have it loaded down with 4 adults and 3 or 4 kids, and being as its a pontoon it needs all the help it can get on holeshot, I was thinking on going to a 4 blade alu prop but thier dosnt seam to be any in a 4 blade in the 7 p or 8 p range, so I it looks like i will have to use a 7 p in a 3 blade . that is of course if i am looking at it correctly any help would sure be appricated
 

SparkieBoat

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3,643
Re: reproping a pontoon

I do not think that they make a 5 pitch..stay with the 3 blade it will increase your max RPMs over a 4 blade same pitch. sounds like you are over loading your motor. you may want to consider a 70 HP motor. you could get a 7 pitch vented prop maybe.
 

MH Hawker

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Re: reproping a pontoon

and your right they dont make a 5 p in any thing that was just a chart i made to see what i thought i would need to put it in the right RPM range. and i belive thats as long as its not out of the 5200 to 5800 rpm range it shouldnt be any over load problems, after all thier thousands of 28 foot toons being pushed around by 9.9. I found a 7 P 4 blade from nissian, and got it on order, that should give it the holeshot to kick it up to speed when loaded up with people and kids, after all its a 20 foot toon lol i use it for night fishing and thats mostly idle speeds, and halling my grand kids around and burning hot dogs, I plan on doing a motor swap next year to put it on a slip at a 9.9 lake and keeping the 40 for when i feel like hitting a bigger lake, I have a 1968 18 foot tridyne west wind, with a 1968 85 Johnson, that kicks along at 45 mph for when i feel the need to move along
 

SparkieBoat

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Re: reproping a pontoon

well I had a 40 on a 28' toon, it was way too slow, I put a 115 on it and was real happy. my dad has a 24 toon with a 60 4 stroke, he is not happy, he wishes he would have gotten the 80 or 115. but in all these cases the motors would run in their recommended RPM range. one thing to check would be to see if you could raise your motor any higher without it venting the prop. also make sure your motor is in good running condition, maybe do a compression, spark and timing checks. also check linkage and make sure you are getting full throttle and that is is all in sync. and that carbs are clean. o yea also make sure your toons are not holding any water.
 

MH Hawker

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Re: reproping a pontoon

well if i was after speed I would add a 90 hp on the back thats the max rating, but its more about just fixing what it has, i am fine with the 40, and ever thing on it has ben inspected and tested and adjusted. the last test was WOT the PO maintained it but not much elese, this is a restoration project mainly to hall my grand kids around and go catfishing at night, you cant beat a toon for night fishing, right now its running around 14 mph gps verified, but has a very slow pick up when loaded down with 4 adults and 4 kids, so a switch to a 4 blade prop, and getting it in the correct rpm range will help a good bit, I am retired and have all day to get there, ill be the old fart cruzing along with a boat load of people and the stero cranking lol and the 40 uses about a gallon a hour at WOT, if it picks up a bit of speed and i expect it will some 15 to 20 thats fine, but im more intersted it it picking up to what ever speed it has when its fully loaded with in 100 yards not a 1/4 mile, at night i mostly idle
 

SparkieBoat

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3,643
Re: reproping a pontoon

I understand, if your motor is in good running condition it should reach the mid to low 5K rpms, I would probably stay with a 3 blade, you will get more RPMs
 
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