fishcop

Decided to ask this question in a new thread due to so many people who just clutter up these threads with negative comments.
One of the culprits were looking at as a potential reason for our lower unit failures is the boat being over propped. Im just wondering what you guys with 400s are running for props, and what RPMs you get out of the motor at full throttle. Weve never seen anything above 5500.

OffshoreApparel.com

So you have 400"s now and keep blowing lowers? How many over what period of time?

plfarrell

Per Mercury's website, it states wide open RPM's as 6200-6800 for the 400. The 400r states 6400-7000.

Think it is safe to say you are way over propped.

Texas 17

It’s sounds like you’re very very overpropped... you should be up around 6800 I believe on that motor.

That’s also the rpm range that give a the extra hp over the 350.


edit: PF beat me to it.

davidwademarine

With 91octane fuel, they should be getting to 6800rpm with a light load in cooler weather. Loaded and during the heat of the summer, 6200rpm is more likely where you’ll be.

MajSchaefer

I was seeing 6500 last weekend running with a fishing load (4 guys).

I run with Rev 4 XPs, 14.6 x 21.

alloyboy

Mercury says to be in the upper half of the RPM WOT range with the boat loaded.

If the WOT Range is 6200 ~ 6800 then you should be above 6500 RPM. Motor trimmed up only to the point of best efficiency and no further.

Over loading a propeller is over loading the motor and also over loading the gear set.

You could very well be on to something to do with your experiencing an excessive number of lower unit failures.

fishcop

Thats what we're thinking now. The boat has never seen a number with a 6 infront of it.

QUOTE=Texas 17;13988753]It’s sounds like you’re very very overpropped... you should be up around 6800 I believe on that motor.

That’s also the rpm range that give a the extra hp over the 350.


edit: PF beat me to it.[/QUOTE]

fishcop

Yep, would love to know what props other guys with big CC are running with these motors. I really think we are way over propped which could be causing this.

QUOTE=alloyboy;13988922]Mercury says to be in the upper half of the RPM WOT range with the boat loaded.

If the WOT Range is 6200 ~ 6800 then you should be above 6500 RPM. Motor trimmed up only to the point of best efficiency and no further.

Over loading a propeller is over loading the motor and also over loading the gear set.

You could very well be on to something to do with your experiencing an excessive number of lower unit failures.[/QUOTE]

fishcop

Yep, thats what were thinkng, and yet weve never seen a number with a 6 infront of it.

ucf_motorcycle

Way overpropped. You would be overpropped at that RPM with the 300 V8 which is supposed to turn 6000.
What boat is this? How many engines? And what prop is currently on them?

willy13

I think the outboards can't even pass the dealer PDI without being propped within mercury specs. So your boat should have never been handed over to you. But this is just my understanding....

alloyboy

PDI performed with one guy and half or less tank of gasoline. Boat gets put into service and everything changes.

Which is why the owner's manual applies to the owner. Not the dealer PDI man.

willy13

yes but his maximum rpm was so low, 5500, I am guessing it didn't reach spec with just one guy.

alloyboy

You could be right.

Travisk

I run Rev4 XP’s, 24P. Don’t remember the exact top end RPMs. I’ll check next time out.

DeepImpact

I’m running quads 400M on a 39 with Bravo FS 27 and with full gas, water, luggage, and 6 people tops between 6200 to 6500 rpms

fishcop

Its a 42 yellowfin with 16 x 19p

QUOTE=DeepImpact;13991705]I’m running quads 400M on a 39 with Bravo FS 27 and with full gas, water, luggage, and 6 people tops between 6200 to 6500 rpms[/QUOTE]

fishcop

Boat is a 42 yellowfin, popped two in the last 50 hours. Both counter rotators

WolpackVO

either you are 6" over propped, not trimming the motors, or dragging an anchor