Quick help-prop!!

[steelespike]

Re: Quick help-prop!!

If its a bare, tiller jon boat it's about 400-500 lbs if its fancy about 800-900lbs.
With you 20 gallons and the motor A 900 lbs jon all up would be about 1600-2000.
I don't see how a 115 couldn't reach 5500.or more. Take a look at the Yamaha performance reports site.
No jons but several tests of boats up to 3000 lbs Smallest props are 17" RPM from 5450 to 6050.
To give you an idea where we are at My 18ft Bare Crestliner 390 lb. utility with a old 25 hp Gale would plane easily, 20 mph, with
6 adults (150 lbs average) and gear. No special prop.

 

[Mi duckdown]

Re: Quick help-prop!!

I don't Know 1 guy, that weighs 115 lbs. Need to read the transom sticker.
Never seen a 18 jon with that much weight unless they where comming from CUBA

 

[travis g]

Re: Quick help-prop!!

You haven't been around many seaarks then. My 1872 was rated at 13 people or 1400#. It was also rated for a 130hp. It's not just a standard Jon. The one I have now belonged to fl fish and wildlife and has a commercial rating.

 

[jestor68]

Re: Quick help-prop!!

The boat weighs 575 lbs without motor.

Motor is about 375 lbs.

20 gal gas is 130+ the weight of the tank.

Add your weight plus gear and you got your operating weight with you alone in the boat.

Eight guys might be around 1200 lbs plus their "gear"; whatever that weighs.

Your motors operating rpm at WOT is 5000-5500 rpm. So, if you barely muster 5000 rpm alone, your dealer is right; you need a 16 pitch 3 blade prop to hit 5500-5600 rpm alone.

But don't expect it to do much when you pack those 8 plus gear in there.

 

[jestor68]

Re: Quick help-prop!!

Something to consider; when I put your numbers(1389 you alone) through the Mercury calculator(running a Merc 115) it tells me to run a 19 pitch Laser II.

That tells me that your Yamaha should be able to happily twist an 18 or 19 3 blade with just you in the boat, if the motor is healthy.

Here are some realistic details from the calculator: 2.07 ratio, 18 pitch @ 5400 rpm equals theoretical speed of 44 mph; with 11 % slip 39.1. It's saying the motor should be able to do 5400 with an 18 pitch. Based on your motor getting 5K with the 4 blade, it should pick up a couple hundred with an 18 3 blade. It's just a couple hundred off the calculators estimate; not too far off.

So perhaps it's not unrealistic to need to drop to a 16 pitch in order to haul those 8 guys around.

 

[steelespike]

Re: Quick help-prop!!

My indication is that the 115 2 stroke has a 2.00 gear ratio.
I agree its possible a 16 is necessary with that load of bodys but you need to figure out why he alone can't reach at least 5500.
1389 is nothing for a 115. My 18 ft Crestliner utility now has a 50 Evinrude with a 19" pitch prop about 1000 lbs all up weight.
It leaps up on the water and nearly flies. No gauges so have to guess about 35 top speed.Calculator says it can't go faster at my guessed 5500 rpm. 2.42 ratio.

 

[travis g]

Re: Quick help-prop!!

8 guys is not the norm but it is when the problem arises. I guess all the opinions (much appreciated) and computer modules, the only thing left to do is slap a prop on and see what's best. I don't expect optimal performance loaded with 1/2 doz people on a noodlin trip. I went with my mechanic, a prop shop and the dealers opinion and decided to try the 16p. The weekend will tell the real story for this boat.

 

[jestor68]

Re: Quick help-prop!!

If your's is the 1872TPCC, it weighs 780 lbs(boat).

 

[steelespike]

Re: Quick help-prop!!

8 guys is not the norm but it is when the problem arises. I guess all the opinions (much appreciated) and computer modules, the only thing left to do is slap a prop on and see what's best. I don't expect optimal performance loaded with 1/2 doz people on a noodlin trip. I went with my mechanic, a prop shop and the dealers opinion and decided to try the 16p. The weekend will tell the real story for this boat.

They are absolutely right a 16" will help the performance and probably needed for that load. But I think it is fairly obvious there is an underlying problem with the lack of performance with one aboard.
One possibility is one or more gauges are not accurate as my calculations seem to indicate.
Being an aluminum jon its possible the bottom is a little slow lots of keels may cause extra drag.
If the tach is or was off you may end up over reving with a 16.

 

[travis g]

Re: Quick help-prop!!

Very well may. I thought maybe the extra drag was from the 4bl. Just gonna have to test different props and see. I know that no two boats can be exactly the same.new tach should tell all. Hopefully get to the lake this weekend and see. I will post results.

 

[travis g]

Re: Quick help-prop!!

Jestor, that's close to it. It is an 1860 side console. Added a larger front deck with 1/4" alum diamond plate. 3 batteries, 2 of which are up front as well as the fuel cell up front. I'm thinking my tach has been reading wrong. Either way the motor bogs with a lot of weight. Just thinking the larger diameter of the existing prop and the added stress of the fourth blade is causing that. Everything on the motor has been deemed perfect by two different mechanics and both say the I have too much prop. Test and tune this weekend hopefully

 

[steelespike]

Re: Quick help-prop!!

Very well may. I thought maybe the extra drag was from the 4bl. Just gonna have to test different props and see. I know that no two boats can be exactly the same.new tach should tell all. Hopefully get to the lake this weekend and see. I will post results.

Good luck, testing will tell.

 

[travis g]

Re: Quick help-prop!!

Ok, here are the results for those that were following. I was horribly wrong/miss led by a few. The boat actually slings the 4bl 18p at 6000 wot with 2 people and fuel tank. The 3bl 16 pitch..... Not even close. Half throttle hit 6k. Looks like I'm back to the drawing board on why my motor bogs with a heavy load of people.

 

[travis g]

Re: Quick help-prop!!

Almost like I need a 3bl 19 to drop my rpm back to around 5500?

 

[steelespike]

Re: Quick help-prop!!

It sure seems the problem is other than the prop.I'm thinking it should be running more prop.Yet retain its power.
To me it points to the motor but it could be a combination of things.
Is the bottom clean and smooth? Are you sure the motor is healthy and tuned correctly?
Are you sure the throttle opens all the way?

 

[steelespike]

Re: Quick help-prop!!

Atre we sure it has a 2.00 gear ratio? At 2.00 a 18 is in the ball park.

 

[travis g]

Re: Quick help-prop!!

I dot know the gear ratio. 18p is in the ball park. Turns it 6000. Looks like I need more prop. Like a 3bl 19?