Prop for better hole shot when people heavy!

[Expidia]

Lotsa questions here . . .

Boat is only 14'9" with the max rated 40 Merc 4 stroke ELPT.

Rated for 660 for 4 people I think. Don't have the rating plaque in front of me right now.

So with the stock prop it runs great with just the two of us. RPM's about 5500 WOT at 33-35 mph.

But rarely do I have 3 full sized adults on board until last week.

Had to move out to the bow area to get it to plane. If another boat came by and threw off a big wake I'd have to start the planing process all over again.

I also hit a submerged log, nicked my skeg (which I'm having a welder fix that) and took a small piece off 1 ear of the prop.

The welder said he can fix that too but I'm more inclined to send it out because I want it in balance so I feel better with a prop shop fixing it.

I'm going to use that one as a spare when it comes back.

I'm going to buy a new OEM one.

The OEM prop that the dealer put on when I bought the boat says on it: Serial # 731-6A40P13 Mercury F10.38X13P

So I take it to mean it's a 10.38 diameter and its a 13 pitch prop?

For the few times I have 3 people on board near the max 660, I'm thinking of buying a 3rd prop to put on for the day to give me a better hole shot. I know I'll lose some on the top end, but I just cruise around at about 22 mph anyway.

Can someone recommend what pitch I should go for the times I have 3 people on board?

Would I need to go with a bigger diameter too?

I also see iboats is asking $147 (seems high to me) for their Quick Silver Black Diamond prop. Is this the equivilent OEM one I have on there now or is their Black Diamond line a better prop thus more money?

It also says it's the one for Merc's from 1977 to present. Does this mean they have made no improvements to the design of their props in over 30 years?



Thx

 

[steelespike]

Re: Prop for better hole shot when people heavy!

First thing we need is the max recommended rpm for your 40.
They like to prop 4 strokes at their max rpm.You don't have to run it there
cruise at your speed but proping that way will help hole shot and load push.
Its possible if you need to reprop it may solve your load problem without prop changing.
Next we need the max rpm and speed with your full load.
If you do need a load prop its fairly easy the motor needs to run within its rpm range.
You will need to lower the pitch (lower number)for the load.
each inch will net about 200 rpm increase.Would be good to try to get in the middle of the rpm band.Let us know what you find and any problems.

 

[Expidia]

Re: Prop for better hole shot when people heavy!

Merc's website says WOT max rpm's is 5500-6000 which is where I am with the 13 pitch prop that the dealer put on.

I'm not looking to tweak the one I have on there now as it does what I want. From what you say I might have to drop down in the pitch range as long as I stay within 5500-6000 when WOT with the load I'm looking to carry?

I might try calling Merc's support as they may be able to zero me in if I can get by with re-propping with one prop and keeping the one I'm having fixed as a spare.

I might not have 3 people on board very soon averaging 200 lbs each. So it will be hard for me to figure the rpm's under a full load.

 

[Expidia]

Re: Prop for better hole shot when people heavy!

So I spoke to another dealer today who gets me my Lund accessories. But he doesn't carry the Mercury line.

He suggested to buy the same OEM prop as I have now for my main prop and have the damaged one repaired by the prop repair shop. He said they can drop the pitch down one size to a 12 when they repair it. This should give me a better hole shot when 3 people are on board.

This way I can change out that prop for the day and also use it as the spare.

He also said I'll probably need to buy a hub kit for the new prop that can be used on future props too.

How does his suggestion sound?

 

[steelespike]

Re: Prop for better hole shot when people heavy!

According to your present rpm you could drop 2 inches and be at 5,900.
It appears that would certainly help your load performance without the chore of changing every time folks come for a ride. perhaps a 11 is extreme.
You may need to throttle back with a light load.Keep the repaired 13 as a spare.

 

[Expidia]

Re: Prop for better hole shot when people heavy!

Thx Steelespike for your responses

I'll pick up a 12 pitch while the 13 is being sent out to be repaired.

I'll check the numbers when I'm running with just the two of us with the new 12 to see if I can leave it on all the time and keep the repaired 13 as a spare as you suggest.

I'll probably be able to swap it for a 12 where I buy it, if I need more torque once I can test it out with 600 lbs of people again.

Clearly, I need to find thinner friends

 

[Expidia]

Re: Prop for better hole shot when people heavy!

Picked up another prop today so I could send my damaged one out for repair. I know I could have got a decent price online, but I wanted one for this weekends boating. Supposed to hit 90 on Sat and Sun.

First place I went to was where I bought the boat. They wanted $146 plus tax for the Quick Silver Black Diamond which to me was a joke.

I've seen it online for $102 no tax free shipping. So I went to another Merc dealer and he sold me the 12 pitch, same diameter as my OEM.

It is the Michigan Wheel line. $69 for the prop and another $40 for the one time hub kit.

I know I could have bought the hub kit for $25 online and I've seen the prop for $55, but I didn't mind paying up for it as at least he had both items in stock and I was able to put it on my rig as soon as I got home. I mailed off the damaged one to an online shop (soderblooms). $28 plus $10 return shipping. I'll use that one as a spare.

Took it out for a test drive on the river. Only me on board, but it pops up on plane real fast. RPM's jump up quickly to 5500-6000. My top end before was about 32-35. Today with new prop I was doing 30 at 3/4 throttle, but at just over 6000 so I have to be careful not to let it over rev.

I was cruising at 23 mph at 4000 rpms today where as with the 13 pitch rpms were around 3500 at 22 mph. But still it was just me today, so it might be different with the two of us when I had the 13 pitch on.

Can't wait to have 3 of us on board again to see if it solves my hole shot to plane at the max 660 weight limit.

This one prop should do it all for me (Thx steelespike) when people load changes without having to keep switching props.

Thx for all the responses.

 

[steelespike]

Re: Prop for better hole shot when people heavy!

I think with your requirements your better off slightly underpropped with the 12 it will do much better with a load. As you said just watch your rpm.
Typically one inch would yield about 200 rpm you must have been closer to 6,000 than 5,500 the specs you quoted in your first post. Let us know your load results.

 

[Expidia]

Re: Prop for better hole shot when people heavy!

Thanks Steelespike
The WOT spec was taken off the Merc website. From my recollection while underway was probably closer to 6,000 as you said.

I'll see how it looks on Sat and Sun as I'll have the two of us on it again. If I'm still close to over revving with the two of us, I'll stick a piece of red tape on the RPM gauge in the form of a red line in case someone else ever drives it with out me in the boat.

And that time would probably be . . . as they say "over my dead body"

 

[Expidia]

Re: Prop for better hole shot when people heavy!

Repaired prop came back today from Soderbloom.com where I sent it. $28 plus $10 to ship back. They did a nice job.

http://

I'll keep this OEM 13 pitch as the spare!

The 12 pitch seems OK to leave on all the time. Still have not tested it under a 3 person load because a third person was to go with us this past Sunday, but we had to cancel the trip due to thunderstorm activity.

So far I find I'm giving up about 5 mph of the top end by leaving the higher pitch 12 on all the time. But I'm probably saving gas because it pops up faster on plane now. So it's a decent trade off for my stlye of boating!