Prop and sterndrive ratio

[Bruce53]

I'm getting a new Mercruiser sterndrive for my SVC 195 SS with the 140 HP engine. While most Stingrays are made for pulling a couple of 200 lb water skiers at 30 knots, I am pulling a couple of 4 lb trolling leads at 3 knots. What is the best prop pitch and sterndrive ratio combination for me? Thanks

 

[Don S]

Re: Prop and sterndrive ratio

Like I said before, keep the same gear ratio. But find a prop with less pitch that will allow you to run approximatly 1000 to 1200 rpm at your prefered trolling speed. This is easier on the engine and keeps the oil pressure up and better oil to the valve train that 6 or 700 rpm.
But you will have to be careful not to overrev the engine, and don't expect to go as fast when you head home at the end of the day or head out for your favorite fishing hole in the morning.

 

[Tail_Gunner]

Re: Prop and sterndrive ratio

Like I said before, keep the same gear ratio. But find a prop with less pitch that will allow you to run approximatly 1000 to 1200 rpm at your prefered trolling speed. This is easier on the engine and keeps the oil pressure up and better oil to the valve train that 6 or 700 rpm.
But you will have to be careful not to overrev the engine, and don't expect to go as fast when you head home at the end of the day or head out for your favorite fishing hole in the morning.

There are few people in this world who give solid advice so freely, you have been just given that,and Walleyehed may take it from here. Ummm you could put a ..........ahh never mind good luck.....

 

[Bruce53]

Re: Prop and sterndrive ratio

Thanks guys. Sounds very logical and I'll do it.....

 

[Texasmark]

Re: Prop and sterndrive ratio

Bruce, you need to get a neck brace for your hole shot......it should be awesome.

I ran 3 sets of numbers using 8" 10" and 12" pitch. You can get your 3-4 mph at 1000-1200rpm with one that shallow, but your top end will be brutal.

What you will have to do is install trim tabs to get the planing speed down as at 4000 rpm with a swag slip of 20% will only give you 13-16-20 mph with a 1.85 gearbox (should be close to what you willl have).

You are really pushing it to the extremes here in trying to hit both numbers.....unless you don't want to ever plane out and I doubt that.

One thing you might do is to go on up to say a 15p which will (should) get you in the 25 mph range on plane but when trolling, tilt the outdrive up 20 degrees or whatever, so that the slip will be high hence the effect of the prop will be diluted by the angle and it may give you your 3 mph at 1000. Would have to experiment on the best tilt angle to suit your purpose.

Mark

 

[Bruce53]

Re: Prop and sterndrive ratio

Problem as I see it: I don't want to "slow the boat" by loading the engine so as to get 3 knots at 1200. The idea was to relieve the load like shifting to a lower gear in a car. Dragging trims, or dragging anything for that matter, will surely cause the boat to slow to 3 knots but loads the engine more. Loading so far below the curve is tough on an engine at something just above idle. Should have gotten a lower ratio, I am thinking, so that the engine would be up in the higher revs. Anyhow, I am only a few miles from the 50 fathom curve and don't really care how long it takes to get there. Good ideas up there guys. Thanks....
You said you "ran three sets of numbers...". What program were you using? I haven't found anything in software that would help me.....

 

[Tail_Gunner]

Re: Prop and sterndrive ratio

Bruce there is no answer for this, you have a motor and a tourqe & rpm curve with only one gear. It's called direct drive, the mfg has selected a prop to utilize both. You need to slow the boat down mechanically aka anchor type of drag system or a new motor with less push

 

[andy1canada]

Re: Prop and sterndrive ratio

Howdy from Canada!

Bruce;

Don't know why someone hasn't suggested a small O/B trolling motor as the solution to your woes...

Granted, they are not cheap but having an auxillary motor to get you and yours home if the main packs-it-in is a good thing; especially if you run on the saltchuck or big lakes.

I'd look at a 10-hp 4/stroke and plumb the fuel to it directly from your main tank.

Too easy.

Happy boatin'!

Terry

 

[Bruce53]

Re: Prop and sterndrive ratio

Bruce there is no answer for this, you have a motor and a tourqe & rpm curve with only one gear. It's called direct drive, the mfg has selected a prop to utilize both. You need to slow the boat down mechanically aka anchor type of drag system or a new motor with less push

Right TG, but I DID have a selection on that one gear. In buying a new outdrive, I could have selected a lower gear. I don't need to do anything to slow the boat other than reduce rpms to about 800. But that is my hangup: I would like to run at a higher (less efficient but kinder) spot on the curve because I may be out for six hours.

 

[Bruce53]

Re: Prop and sterndrive ratio

Howdy from Canada!

Bruce;

Don't know why someone hasn't suggested a small O/B trolling motor as the solution to your woes...

Granted, they are not cheap but having an auxillary motor to get you and yours home if the main packs-it-in is a good thing; especially if you run on the saltchuck or big lakes.

I'd look at a 10-hp 4/stroke and plumb the fuel to it directly from your main tank.

Too easy.

Happy boatin'!

Terry

That is the best of all solutions except for one little factor: $$$ I am retired navy and don't have a lot of that stuff.....

 

[Bruce53]

Re: Prop and sterndrive ratio

Like I said before, keep the same gear ratio. But find a prop with less pitch that will allow you to run approximatly 1000 to 1200 rpm at your prefered trolling speed. This is easier on the engine and keeps the oil pressure up and better oil to the valve train that 6 or 700 rpm.
But you will have to be careful not to overrev the engine, and don't expect to go as fast when you head home at the end of the day or head out for your favorite fishing hole in the morning.

New prop with less pitch is surely the answer. A lot cheaper than a new kicker although it would come in handy in emergencies. And the gear is there to stay of course. You said you "ran three sets of numbers...". What program were you using? I haven't found anything in software that would help me.....

 

[Bruce53]

Re: Prop and sterndrive ratio

Like I said before, keep the same gear ratio. But find a prop with less pitch that will allow you to run approximatly 1000 to 1200 rpm at your prefered trolling speed. This is easier on the engine and keeps the oil pressure up and better oil to the valve train that 6 or 700 rpm.
But you will have to be careful not to overrev the engine, and don't expect to go as fast when you head home at the end of the day or head out for your favorite fishing hole in the morning.

New prop with less pitch is surely the answer. A lot cheaper than a new kicker although it would come in handy in emergencies. And the gear is there to stay, of course. You said you "ran three sets of numbers...". What program were you using? I haven't found anything in software that would help me.....

 

[Tail_Gunner]

Re: Prop and sterndrive ratio

I'm getting a new Mercruiser sterndrive for my SVC 195 SS with the 140 HP engine. While most Stingrays are made for pulling a couple of 200 lb water skiers at 30 knots, I am pulling a couple of 4 lb trolling leads at 3 knots. What is the best prop pitch and sterndrive ratio combination for me? Thanks

Simple enough 16pitch 4 blade, but your bow is going to steer you all over the place. the prop may cost you 90.00 but you could alway's hang a couple of 5 gallon bucket's off the back and get the same result's........... you must be a Norwegian....

 

[Bondo]

Re: Prop and sterndrive ratio

Ayuh,......

You're Trying to do what Can't be Done.........

The 3.0l comes With the shortest Gear set there Is,....... 2:1........
There Ain't No Lower.........
Props that Fit your drive are Only available down to a 15" pitch,.....
That Won't get you to where you Think you want to be Either.....
And,........
You're putting More into Loading it than is really There.......

Your engine,+ drive will Like it Much Better,.... If you run Trolling Socks, 5 Gallon Pails, Over extended Trim Tabs, Or Whatever you care to Drag to slow it down........
That'll allow the driveline to Load up,+ stay that way,.....
Trolling with the driveline constantly Loading,+ Unloading is Hard on the engine Coupler,+ Everthing else in the driveline......

In Other Words,....... Your Thinking on getting your Speeds Down,+ RPMs Up,.....
Isn't How it's Done...........

 

[Texasmark]

Re: Prop and sterndrive ratio

Bruce, in response to your question to me, I use the BAM prop slip calculator on www. Like I said, you are asking for two extremes that are not easily met (if at all) the way you want to go about it.

Mark

 

[Bruce53]

Re: Prop and sterndrive ratio

Thanks Mark, Bond-O and all.... You convinced me......

 

[QC]

Re: Prop and sterndrive ratio

You're putting More into Loading it than is really There.......
..

Just to double this up. The problem with Marine engines at idle and low speeds is not enough load . . . I wouldn't think about load for another nanosecond. Load the snot out of it. You'll get a little more heat in the engine (good) and possibly get the R's up slightly too, also good.