Mercruiser 350 Prop Max.-

[Sea Rider]

Scenario :

A friend of mine just bough a new 24" powerboat equipped with a new generation Merc 350 IB. He doesn't know much about engines bessides they run on fuel. The factory delivered prop which he doesn't know about its diam nor pitch broke while hittting a submerged object, that's the issue about boating near not known seashores. The boat seller gave him according to his words a "force/work prop", doesn't know its characteristics neither. It's already installed and boat is on water.

Tells me that passing middle throttle rpm to wot the engine won't rev passing 3.0 K rpm, which dangerously luggs the engine. Wild guessing, which diam/pitch should he start with ? He usually uses his combo light to medium loaded. Will check if possible to have a look at the old prop, get more info on the engine model and boat's dry weight.

Happy Boating

 

[steelespike]

Is this a straight inboard. Is the there any gear reduction?V drive? Is it a 3 blade?

 

[Sea Rider]

Is a straight IB the ones located aft with sterndrive comming out engine ? If so, then yes. Will need to check with combo seller those specs, don't want my friend screwing his new engine boating that awful way.

Happy Boating

 

[Bondo]

Is a straight IB the ones located aft with sterndrive comming out engine ? If so, then yes. Will need to check with combo seller those specs, don't want my friend screwing his new engine boating that awful way.

Happy Boating

Ayuh,.... So it's an I/O, a sterndrive, 'n Not an Inboard,..?? Mercruiser,..?? Volvo,..?

Yer Bud needs to look over the prop he wacked to find the numbers stamped into it to see where ya wanta be,.....

 

[Sea Rider]

Yes, it's a Mercruiser 350 V8 5.7 Ltr 5.0 EFI sterdrive 1:47 gear ratio engine. Been checking props at Iboats and there's 16 different pitches to choose, pitch goes from 11 to a 28. Should I select a middle number prop, lets say 20 pitch prop good for light weight applications for a 2 ton 30 footer power boat as a starter prop in case shot originall factory delivered prop was already thrown into the blue ?

Happy Boating

 

[Bondo]

Ayuh,.... I Guess you could do that, but it'd be awhole lot easier to just Read the Numbers off the old prop,.....

 

[Sea Rider]

Prop isn't available, was thrown into the deep. Which starting point pitch prop would you choose and go from there dialing best prop depending on the wot rpm numbers achieved on a wot test with lightly loaded boat.

Happy Boating

 

[Bondo]

Ayuh,.... They generally run odd numbers, so a 19" or 21" pitch I guess,.....

 

[steelespike]

If the dealer is willing to let him try props then a 19" makes sense.
Does he understand about trimming down for hole shot? If the boat wasn't planed out then you couldn't use the loaner prop as a reference.
At 3000 rpm you would need to drop 9" to get to 4800 rpm So I'm thinking the boat wasn't planed out.

 

[Sea Rider]

That's why need to go out with boater and make a wot test on flat no wind sea cond, boater does not understand prop issues that could screw his engine at wot besides filling tank with fuel. Owner said it was a 30 footer, to me looks as a 25-26 max. Will check that out during weekend.

Happy Boating

 

[Sea Rider]

Update,

The original prop mounted on a Bravo 1 sterdrive was a 19 pitch prop. A pitty that owner didn't make a wot test with current delivered prop to check if at least middle to max rpm while lightly loaded and going from there for a prop maximization if needed. It's a must tach current props factory delivered with engines, in case you break it will know if replacing for same model or go for a prop optimization to be revving at max revs the engine is capable.

Happy Boating

 

[Sea Rider]

Finally went with boat owner for a wot spin on near calm slight wind open waters. Combo was lightly loaded with just 2 up and 1/4 fuel tank. He doesn't know which prop pitch he's using so neither do I. Scenario at 3/4 throttle engine won't rev passing 4100 rpm, at full wot engine rpm just stays there. Combo response is slow to plane fast. Owner did not previously tached the 19 prop pitch factory delivered due to breaking it before engine was broken in to know if being inside safe wot parameters which are 4800-5200 rpm.

Would it be wise to go for same19 prop pitch or one less ? How much more rpm varies going from19 to a 18 pitch, both props being same size ? BTW, who said that by dropping one less pitch there's a 150-200 rpm gain ? Does this statement applies to any given engine powering a lightly boat ?

Happy Boating

 

[Maclin]

Best to find out exactly what is on there now that gave you that performance don't ya think?.

 

[Sea Rider]

For that to happen will need to take boat which is not small out of the water with crane or hire a diver to have a look at prop, besides combo is not mine and don't think owner will like going that route.

Happy Boating

 

[Sea Rider]

How much rpm, hole shot, top speed whatever will a 14 1/4" 19 pitch prop gain/lose versus same 14 1/2" version. First is a Hustler, second is a Quicksilver Black Diamond ? The plan is to put back same size pitch factory delivered prop with engine which was not previously tached due to breaking it when hitting a solid under water objetc. So this will be a starter prop and then go from there if combo needs a prop maximization.

Happy Boating