Prop size/pitch selection

[marcortez]

Yamaha F60 LTR 20" shaft, current year model, will be mounted on a older Mexican style panga 22' open, flat bottom skiff with remote steering.
Total weight, including boat, motor, fuel and gear should be around 1200 to 1500#.

These pangas are narrow in the stern and I am confident not designed for the additional weight of a 4 stroke, over an older 60-70 2 stroke which were common back in the days.

I do not have a need for top end speed performance and would be happy with a "all round" prop, as long as it allows the motor to reach it's maximum RPM of 5000-6000 RPM.

I am leaning towards a 4 blade aluminum, as my research tells me that style prop will give some "stern" lift....which would be a good thing I believe, due to the weight being mostly aft.

The engine selling dealer is suggesting a 6H5-45952-00-EL Yamaha OEM 10 5/8ths by 12" pitch 3 blade aluminum.

I live in Mexico and am 700 miles away from this dealer, so obtaining the correct size prop is imperitive the first time around.

Suggestions..........

 

[steelespike]

Re: Prop size/pitch selection

I don't have a lot of confidence for a 4 stroke doing well with a stern heavy boat
whose design may struggle.I would lean toward the dealers suggestion as they are probably aquainted with both the motor and style of boat.Though a 4 bld 11 would probably do better.Go with the 11 4bld. or the 12 and replace it if the performance indicates it.You should probably have a spare on hand anyway.
If you end up under propped with the 11 4 bld you can still use it just watch the rpm. then add a prop based on your performance.

 

[hwsiii]

Re: Prop size/pitch selection

Marc, you don't mention anywhere how much extra weight will be in the boat for the Normal load you are carrying. This is very important as it will be directly proportional to the pitch and the thrust that is required from the prop for this boat. If you will take about 5 pictures of the boat, as well as tell me how much weight above the aforementioned base weight you will normally have in the boat, we can then decide on a prop.

I find the motor to be 60 cubic inches, so the normal torque loss experienced by a 4 cycle versus a 2 cycle should not be as bad as it could be. But yamaha took advantage of this and raised the lower gear ratio to 1.85:1 instead of the more normal 2:1 or higher ratio. You should not expect to have a lot of hole shot or acceleration with a 3 blade prop, I believe you will be much better off with a 4 blade prop, for the extra thrust it provides, as your hole shot will be much better as well as your acceleration should be fine.

Depending on the extra weight you have in the boat I expect you to be able to do about 30 MPH if you aren't carrying too much weight.



H

 

[marcortez]

Re: Prop size/pitch selection

Sorry no photos right now as I have not bought the boat yet.

What I can tell you is this:
length 22'
beam 70"
weight <800#-1000#> 6 degree deadrise at the transom.
open skiff style with no frills. a "true" Mexican panga vs the "gringo" models which are all tricked out.
basic side console with remote steering
a 60 hp yamaha weights 240#
12-15 gallons of fuel in a remote tank (90# w/15 gallons)
12v starting battery....50#
14 gallon live bait tank @ 125#
add 215# for me and 180# to 200# for a buddy on occasion.
4 rods/reels/assorted angling gear. 50#
I come up with under 2000# total. boat/motor/gear

the stern narrows down to less than the widest beam amidships....this is what I meant by heavy on the stern. it is NOT beamy aft, hence less floatation support as compared to amidships.

Most pangas here (Baja Sur, Mexico) are equipped with 75's or 90ties.
A 60 is a $1000 bucks cheaper and weights 100# less and seems to be better on fuel usage.
High speed is not a concern. I would be quite happy at 25 mph cruise on flat water.
Exchanging the prop out for another is not easily do-able down here in the hinterlands. It's 700 miles to a dealer in San Diego.

see this utube video and it will show you the basics...same setup only with side console remote steering.
http://www.youtube.com/watch?v=mBAmQKq4NyA

thanks for your help

 

[hwsiii]

Re: Prop size/pitch selection

Marc, I have been considering building a panga 25' for over a year now, and I am including a drawing of it, but mine is a much deeper Vee than yours, so I know the hull forms very well.

Panga 25

I will take the information you gave me and run some numbers and get back with you.



H