Prop Load out? What is the formula?

[Sirmarsh]

New here, and looking for some prop help.

I have a 2001 Quicksilver 430HD sib w/ 2001 Tohatsu 25C3.

I'm having issues, after getting on to plane. That's all the boat will go, just on plain and nothing above. It feels like there should be more *go* but it just cruises along at what feels 11mph.

The motor starts and idles just fine. When I got to WOT, there just is nothing there past getting my sib on plain. I have ulta-sonic cleaned the carb 5 times, pulled the jets, not 1 spot of dirt or anything. Order a carb rebuilt but didnt use it because the carb is so clean.

I pulled the plugs and replaced(no issues) and replaced them. Drained the gear oil 3 times. No issues.

I was reading some posts here, and I seen were the hub can come into play for slipping.

Here is my question.

When buying a new prop, the tohatsu website claims that a 25hp prop goes by load?

So, if I have a 1000lb load out, how do people run higher pitch?

0-500lbs should use a 13,14 pitch
500-1500 should use a 12,11 pitch and so forth.

So....if my sib is 246lbs, motor is 109lbs, me 240, gas, cooler and a some friends + 500lbs, do I need to go by the weights of the load out for a lower pitch? How are people hauling a jon boat with 4 guys and gear on a 13p prop and NOT hurting the motor? Is the 500lb weight limit for the 13p is when it could cause the hub to slip?


I bought a 10in 12p prop from here in hopes this will work. I think a sib w/ 25hp should be in the upper 25+mph, but it seems like I could swim faster then what my boat goes.

Is this a prop issue or am I chasing ghosts here?

I do have a tiny tac on the motor, still trying to figure out the settings. I looked down at the rpm during one of my tests, and it was reading 7200+ rpm, but sounded like it was in the 2000 rpm range.

I never *hear* my engine wind out like a normal outboard. It starts to...plains out...and then just holds there. If i let up even the slightest in rpm, I lose a lot of speed.

Can anyone help me here?

Am I missing something here in prop engineering?

 

[jestor68]

Re: Prop Load out? What is the formula?

That chart in your owner manual is only a general guide for choosing the correct prop.

The ONLY correct way to do it is to prop the motor so that it operates within it's WOT rpm range(5000-6000 in this case).

You must have a ACCURATE tachometer to accomplish this.

Double check the setting(s) on your Teeny Tach, and/or have the dealer hook up his shop tach to verify your tach readings.

According to the web site, your RIB weighs 267 lbs; with motor 376 dry weight. Not clear on the people and gear weight(your 250 + 500 lbs?) plus gas?

The Mercury prop selector(using a Mercury 25) says a 10 pitch and engine tests(again Mercury 25) pushing similar weights used a 9.75 X 9.5 pitch prop to go 26 mph at 6000 rpm.

It appears that my gut feeling of a 10 pitch prop might be on target.

 

[Sirmarsh]

Re: Prop Load out? What is the formula?

Thanks for getting back with me so quick.

I did order a 12p prop from iboats before posting and reading your reply. Should I cancel and go with the 10p then?

In the last post I mentioned my weight plus the 500lbs. I would be using this mainly for me(250lbs) wife(105) and 3 small kids(90lbs,50lbs,60lbs) plus coolers, chairs gas to go to our beaches on the Mississippi.

Some times I do take the guys out(5) total all 240ish lbs, and would like to stay in the 20mph area loaded down. I was thinking the 12p because the website said 500-1500lbs. I'm taking that statement as the motor has to push itself, boat, people, gear, gas with a total weight of no more then 1500lbs. Is this not how to look at this issue? So boat,motor + myself are easy 500lbs, leaving an extra 1000lbs for my load out.

I'm confused, but welcome your advice.

 

[steelespike]

Re: Prop Load out? What is the formula?

Stick with the 10" pitch suggested.Its unlikely your rib will plane with 1200 lbs of guys in the boat.
I wonder what the rating on the boat is? What size is the boat?
Is the motor trimmed down (prop closer to the boat) when testing?Will it plane with just you in the boat?
What size is the present prop?

 

[Sirmarsh]

Re: Prop Load out? What is the formula?

The rating for the boat is 2206lbs or 2206lbs @ 14ft. Motor is in the 3rd setting from the Transom. I tried all the settings and that seemed the best to get the boat up and out of the water. It is a 13p on it now w/ a bent blade. It gets on plane with me and 1 other(240lbs ish guy) but that is all. Past that the engine just *stays* at the constant rpm and never revs up to what I think would be it's full potential if you know what I mean. I never hear the engine wind out, and that is my quest to fix. I just hope it's a prop issue.

 

[Sea Rider]

Re: Prop Load out? What is the formula?

Sirmarsh,

You need to reset TT factory setting to 2 sparks per revolution, if not, tach will read strange out of this world numbers. Place in stand by your prop order.

It's a must need need to know if you are experimenting a spun hub before moving to other pitch prop, or buying blindless one. Perform the hub slip test before doing any other things, including fingering the whole engine with no positive results whatsoever. What's the max HP transom rated for that size sib ?

A 25 lacks top punch running on a 430 sib. Meantime, remove engine cowl, place gear lever into forward, fully thottle...is your carb achieving full 180? butterfly opening ? Is white roller stopping at small groove on cam ? if so, will need a engine HP optimization to improve the "go"..:lol:

Happy Boating

 

[jestor68]

Re: Prop Load out? What is the formula?

The rating for the boat is 2206lbs or 2206lbs @ 14ft. Motor is in the 3rd setting from the Transom. I tried all the settings and that seemed the best to get the boat up and out of the water. It is a 13p on it now w/ a bent blade. It gets on plane with me and 1 other(240lbs ish guy) but that is all. Past that the engine just *stays* at the constant rpm and never revs up to what I think would be it's full potential if you know what I mean. I never hear the engine wind out, and that is my quest to fix. I just hope it's a prop issue.

I think what is causing your confusion is the notion that a boats capacity rating means that it will perform at that weight.

It won't. That just means that it should not sink with that much weight in it.

The web site says it has a capacity of 8 people. It would never plane off with 8 people in it; but it should not sink.

You put whatever pitch prop you have to in order to get the motor to run at WOT at the mid to upper part of it's rpm range ( 5500-6000 rpm) with the "normal" load in the boat.

The ONLY sure way to select a prop is through on the water testing with a accurate tachometer.

 

[jestor68]

Re: Prop Load out? What is the formula?

Another thing to bear in mind with this type of boat is the type of bottom it has.

Quicksilver boats have two types of bottoms; a "soft bottom" and a "rigid bottom".

Your 430 HD is a "soft bottom", and will not perform like one of the "rigid bottom" boats; meaning it won't go as fast because it lacks the rigid glass hull that the other types have. It's like trying to push a large tube over the water; lots more drag than the rigid bottom type has. See the rigid hull of the Amanzi CC. The Ocean Runner has a similar hull.

 

[Sirmarsh]

Re: Prop Load out? What is the formula?

Thanks so much for all the info. I'll try and place my order on hold.

I'll get to the water next week and try to test the prop as described. I'll post back my findings, and will reset the TT.

Thanks again, it's starting to make sense

 

[Sirmarsh]

Re: Prop Load out? What is the formula?

Just a after thought, I really like this engine. Very low hours, seems to run perfect...should I sell the 430HD and go with a little jon boat then for what I am wanting to do? Putt-putt around on the water with friends, no fishing, no tubes, just people+coolers going to the beach.


I could sell my sib on CL for around 800$ and can pick up a hull for around the same...

 

[Sirmarsh]

Re: Prop Load out? What is the formula?

Was able to get to the water last night and test.

Put a 12p prop on, no difference then before. Reset TT and is now reading correct. Idle is around 840rpms(Book calls for 900), but WOT is only at 3900. Starts fine, idles fine, no sputtering nothing. Just for some reason, it starts to go, and you think, this is going to be fun...then just stops at 3900rpm. I never hear the engine rev up....just bzzzzzz at 3900rpm....What could be causing an engine to only go to 3900 under load? In N, it will hit the limit no problem. Took hood off while running, carb is open and getting fuel. New plugs, new oil, new gas.

There has to be something I'm missing here. Can anyone give more advice as to where I should start troubleshooting.

 

[pootnic]

Re: Prop Load out? What is the formula?

I think people already answered your question.
Your props to big for that style boat and the load your looking to haul.
Are you maxed out,on the recommended hp for that boat(whats the boat rated for)?

 

[Sea Rider]

Re: Prop Load out? What is the formula?

A 430 sib is a excellent size for your intended boating fun, just needs to be fully air pumped to it's factory recommended working pressure to perform as expected. When at forward and full throttle, does white roller stops at which (1-2) pic ? check. If stoping at 1, need to upgrade the engine to 30 HP for peanuts cost to have extra 5 HP punch to better move that 430 at wot. Will plane much faster, then you can reduce throttle and maintain plane with less fuel consumtion. Nobody in it's right mind goes full wot all the time...

If stopping at 2, you have a spun hub or need to raise revs quite a bit by going pitch down. That engine should be wot reving at 6,000 rpm, 3,900 is quite low, you're lugging the engine. How many prop pitches can you choose besides a 12", 11-10-9 ?

Happy Boating

 

[Sirmarsh]

Re: Prop Load out? What is the formula?

A 430 sib is a excellent size for your intended boating fun, just needs to be fully air pumped to it's factory recommended working pressure to perform as expected. When at forward and full throttle, does white roller stops at which (1-2) pic ? check. If stoping at 1, need to upgrade the engine to 30 HP for peanuts cost to have extra 5 HP punch to better move that 430 at wot. Will plane much faster, then you can reduce throttle and maintain plane with less fuel consumtion. Nobody in it's right mind goes full wot all the time...

If stopping at 2, you have a spun hub or need to raise revs quite a bit by going pitch down. That engine should be wot reving at 6,000 rpm, 3,900 is quite low, you're lugging the engine. How many prop pitches can you choose besides a 12", 11-10-9 ?

Happy Boating

Thanks so much for getting back with me. I do believe it is pic 2 with the roller at the end. I put the prop(could not stop the order from iboats) 10in 12p and it does 3900rpm. I'm going to try to put the 9.8in 13p back on it and see if the rpms drop more. They should in theory if nothing is wrong with my motor. My main concern now is, I'm missing 2100rpm. No prop is going to fill that gap is there? I could only go down to an 8 on this motor. Say I get the most rpm per pitch downgrade(200rpm). From 12p to 8p the diff is 4, so total 800rpm I *might* gain. Is this correct? I'm still off 1100 rpm somewhere. The 12p prop coat 74$. The 8p prop is 98$. Hate just throwing money at this problem.

Pulled the plugs when engine is running for both spark plugs. Both times the motor stopped as it should.

Do I throw another 100$ at this boat and go to a 8p, and just offer up the 1100rpm the River-Gods?

 

[Sirmarsh]

Re: Prop Load out? What is the formula?

After doing a search on the conversion from 25hp > 30hp on this engine, it is just removing the restrictor plate on the carb. 25/30hp Tohatsu come *timed* the same.

 

[Sea Rider]

Re: Prop Load out? What is the formula?

Will depend on the rebadged brand too specially same 25 Mercs, yes will need to swap carb gasket for the 30.model, will breath more air and along + 5 nore timing advance will have a converted 30HP.

You must be 100% sure butterfly is opening all the way. Remove cowl, move lever to forward, with left hand finger raise roller all the way till stops, with right hand throttle grip fully, end of can must contact roller. Without releasing roller, rotate grip back and forth (less than middle throttle, ) cam end hould slightly bang against white roller, if it's correct Ok,

Before throwing more money on props check gasket and can/roller issues,

Happy Boating.