I don’t think my boat is hitting the speed it should

[JimS123]

Well I stand corrected. I remember the 135, but I thought there was an interim 130 as well.

Nevertheless, the 1992 Mercruiser catalog also listed a 115 HP 3.0. That year the 135 was a 3.0LX.

 

[Chopp]

At least when I bought the boat and looked it up on nadaguides.com it listed it as 115hp. So I got my 19p back today, and the boat did 37mph and I didn’t notice the rpms drop much. It was around 4800-4900. The engine itself says 4200-4600 on it. So I was thinking, get rid of the 17p and I’ll use the current one for tubing, but for general usage, I was thinking of a stainless 4 blade. I know steel doesn’t flex as much. But what size should I go for a 4 blade stainless? I’m fairly confident I can get this boat to 40mph.

 

[Chopp]

I should note, I hit that speed with a half a tank of fuel which is like 5 gallons and fishing gear, along with myself and a buddy. Us together are around 450 pounds.

 

[QBhoy]

You might just be close to spot on if you don’t include all the gear normally.
to be honest I don’t know if this 3.0 with 115hp never heard of it in recent times. Not to say there isn’t one, but can’t be common. Also the 3.0 I know Of has a range of 4400-4800 I’m sure.

 

[jimmbo]

Going to a 4 blade will kill your Top End,

If your engine has a Sticker on it that say 4200 - 4600, that's what you go with. You are a bit under propped, so adding 2 more inches should drop the RPM by about 400 which should place you around 4400 - 4500, which is okay. The Holeshot will be slower.Your Top Speed might go up a MPH. Any Idea what brand the current prop is?

Don't put too much in the "AL blades Flex" statement, While there may be a some flex, it would be in the range of less than 1/100", but hey, it has Sold a lot of SS props. Of course there will be someone spouting about Harmonics due to the Flexing and so forth,,, But AL props generally have fairly thick Blades, and the Aluminum used for props is not really a Elastic Alloy

Switching to a SS, brings up a bunch of Variable. If the Prop is just SS version of the AL, it will be heavier and more Durable. If the Blades have been thinned, it will be slightly more Efficient, and you may end up with a bit more speed or Thrust as Slippage is Reduced, however with less Slippage, the engine has a Higher Loading, and RPMs may drop a wee bit, cancelling out most or all of the Theoretical Speed gain. If the SS Prop was designed with a more advanced Blade Design to take advantage of the SS Alloy, the Blades may have a Different Shape, Rake and Cupping. These changes will affect Holeshot, Top Speed, Handling, and even how the Boat rides in/on the water.

Best way to get more speed with out swapping to a 4.3 is to make sure the Hull is Straight, with no Hooks, is Smooth and clean of Algae, or Barnacles, remove all unneeded Ballast, place loads for best Performance, and use the Power Trim correctly.. Being an I/O, Outdrive Height is not easily adjusted, you just have to hope the Boat Maker got it right.

 

[Chopp]

Going to a 4 blade will kill your Top End,

If your engine has a Sticker on it that say 4200 - 4600, that's what you go with. You are a bit under propped, so adding 2 more inches should drop the RPM by about 400 which should place you around 4400 - 4500, which is okay. The Holeshot will be slower.Your Top Speed might go up a MPH. Any Idea what brand the current prop is?

Don't put too much in the "AL blades Flex" statement, While there may be a some flex, it would be in the range of less than 1/100", but hey, it has Sold a lot of SS props. Of course there will be someone spouting about Harmonics due to the Flexing and so forth,,, But AL props generally have fairly thick Blades, and the Aluminum used for props is not really a Elastic Alloy

Switching to a SS, brings up a bunch of Variable. If the Prop is just SS version of the AL, it will be heavier and more Durable. If the Blades have been thinned, it will be slightly more Efficient, and you may end up with a bit more speed or Thrust as Slippage is Reduced, however with less Slippage, the engine has a Higher Loading, and RPMs may drop a wee bit, cancelling out most or all of the Theoretical Speed gain. If the SS Prop was designed with a more advanced Blade Design to take advantage of the SS Alloy, the Blades may have a Different Shape, Rake and Cupping. These changes will affect Holeshot, Top Speed, Handling, and even how the Boat rides in/on the water.

Best way to get more speed with out swapping to a 4.3 is to make sure the Hull is Straight, with no Hooks, is Smooth and clean of Algae, or Barnacles, remove all unneeded Ballast, place loads for best Performance, and use the Power Trim correctly.. Being an I/O, Outdrive Height is not easily adjusted, you just have to hope the Boat Maker got it right.

My current prop is a 14.5x19P Merc. Black Max, the gear I gave is the normal amount I carry, it’s not much. I play with the trim and do it the best I can. The hole shot is okay, it’s the same as my buddy’s 2014 17ft Alumacraft with a Suzuki 140HP outboard. I’m just not entirely too sure what prop to go with. I would like to get rid of slippage and try to get the best top speed prop as most of my time on the boat is on a lake by myself or with someone else. Once it warms up and I do tubing with the entire family on board then I’ll see if the 17P or this 19P is better.

 

[QBhoy]

If you’re after speed...you don’t want a 4 blade. That’s for certain.

 

[Chopp]

If you’re after speed...you don’t want a 4 blade. That’s for certain.

Good to know. I’ll see if I can try some props, if not then I’m thinking the Merc Vengeance prop?

 

[QBhoy]

Good to know. I’ll see if I can try some props, if not then I’m thinking the Merc Vengeance prop?

In my opinion, the vengeance is a waste of good money. Just a shiny looking black max but heavier.

 

[jimmbo]

Once it warms up and you load the boat Up, the 17 might be the right choice.

You can't get rid of Slippage, it is needed to propel the Boat, Slippage needs to kept at reasonable levels, 10 - 15% is acceptable for a Planing Hull, On non-planing Hulls 50+% is still acceptable, only on very Light and Fast Hull designs is less than 5% slippage attainable. I will be waiting for someone to claim his boat is getting less than 2% slip. Well, allowing for Tach Inaccuracy, and Speedometer error(including GPS inaccuracy due to Currents, and the fact a prop may not be 'Exactly' the Pitch stamped/cast on it, the math might work out to it. Heck, there have been Boaters claiming Slippage in the negative Numbers.
All other thing being Equal, a Prop with More Blade Area will generally have less slip, yet will have a Lower Top Speed. Myself ,if I could get a 2 Blade Prop for my Boat-Engine, you wouldn't see my Departure to get if, because of all the Dust

 

[jimmbo]

In my opinion, the vengeance is a waste of good money. Just a shiny looking black max but heavier.

QBhoy... are WE going to say the 'E' word?

 

[QBhoy]

QBhoy... are WE going to say the 'E' word?

. Trying not to.....if you do, I will...

 

[JimS123]

The stock alum Black Max gave me 12% slip. An "E" dropped the slip to 8% with no other change. Gotta love SS.

If you get negative slip it must be because the engine is running without using fuel....LOL.

Maybe the OP should check his slip and report back. If the number is good maybe the prop is already optimum.

http://www.mercuryracing.com/prop-slip-calculator/

 

[Chopp]

The stock alum Black Max gave me 12% slip. An "E" dropped the slip to 8% with no other change. Gotta love SS.

If you get negative slip it must be because the engine is running without using fuel....LOL.

Maybe the OP should check his slip and report back. If the number is good maybe the prop is already optimum.

http://www.mercuryracing.com/prop-slip-calculator/

It says my slip is 17% at WOT and if I’m at a cruising speed on plane, which is about 22mph at 3300rpm, the slip is 27%

 

[JimS123]

Its not far outa line. The bimini is probably hurting you some. Its an old boat. I guess I wouldn't worry about it. Just go boating and have fun. If it meets you're requirements, then all, should be good.

 

[Chopp]

Its not far outa line. The bimini is probably hurting you some. Its an old boat. I guess I wouldn't worry about it. Just go boating and have fun. If it meets you're requirements, then all, should be good.

The 37mph at 4900rpms I hit is without the Bimini and 3 people aboard. I guess my point is running 2 props, 1 for a fully loaded boat doing water sports and the other for myself or maybe another that I need to be in the WOT range. I’m 300 rpm off. And the rpms and speed doesn’t really change whether it’s me or 2 more. My local shop doesn’t let you try out props, so I’m asking what you guys suggest. I think a 21p might be a bit much, I don’t think 20P is a thing so maybe there’s a prop that has more aggressive cupping? What’s your input?

 

[JimS123]

Personally, for me having to change props would be a deal breaker - just too much hassle. We did it in the old days but that was just us kids liking to play around.

If it were my boat I would switch to a 19" SS prop. That should bring the top end in range and you shouldn't lose speed or hole shot.

 

[Chopp]

Personally, for me having to change props would be a deal breaker - just too much hassle. We did it in the old days but that was just us kids liking to play around.

If it were my boat I would switch to a 19" SS prop. That should bring the top end in range and you shouldn't lose speed or hole shot.

Took the entire family out today with 5 people in the boat, hole shot wasn’t that great at all but nobody was sitting in the bow. It still went to 4800-4900 rpms and hit 36.5. It’s odd to me... but what model SS Merc prop do you recommend?

 

[JimS123]

First weigh the boat to be sure its not waterlogged and worth investing in. SS is expensive.

Earlier several posters alluded to a Mercury SS Enertia prop. I bought one last year and wholly crap, what performance!

If your "not great" hole shot means it takes a few more seconds to plane (as opposed to it won't plane at all) then maybe a Doelfin would help.

As previously posted, my last boat with a 3.0 had a prop repitched to give the full 4800 rpm, fixed trim tabs and a Doel to boot. With 3 fat adults, 1 skinny adult and 4 skinny pre-teens (8 people) it would come up on plane in an instant.

Although I'm an outboard guy now, I was always impressed with the performance of the 3 liter 4 banger. Just need the right prop.

 

[QBhoy]

To be honest you are never going to see silly speeds with this boat and although a good prop can make a world of difference, I wouldn’t spend silly money on one like and enertia. I have never known anyone with an enertia on a 3.0. They usually like to perform best on a hull with some moderate performance traits to it and a fair bit of power to turn it.
Personally, I’d be sticking a laser 2 on it and go enjoy yourself.