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Old 01-18-2015, 05:40 PM   #1
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Re: deliberate overpropping

With more articles and more knowledgeable people coming out in favor of deliberate over propping I foresee future problems related to this other than actual engine damage. I suspect most attempts at emulating the process will be made by individual boat owners trying to squeeze a little more speed or economy out of their rig. There will be some builders such as the people building the Great Harbor boats applying this concept on their new builds, but for the most part their will be little real testing documentation or accountability involved. I doubt that there will be mechanical stops on the throttles or changes in governors to regulate attainable RPM levels in order to avoid real significant overload. Basically the idea would be to set the prop and engine to operate in a safe range of RPM where at higher RPM the motor would be significantly overloaded and exposed to damage. What happens when one of these DIYS boats comes on the used market? A standard sea trial on such a boat would come up with significant over propping and cause for many to walk. Short of an expensive engine survey which might include some tear down how would the new buyer know what's what? What if the Owner dies and boat goes to a broker and is sold or transported a few hours away and run hard? How many of us want to buy a used car where the previous owner tinkered with the motor's electronic control system to change the performance? I would think if a real value to over propping becomes apparent it would be a good thing if some standardization comes into play and the motor manufacturers chime in with optional controls and parameters to accommodate an improvement in performance on certain boats otherwise it's a bit of a free for all.
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Old 01-18-2015, 06:16 PM   #2
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Boating is a bit tricky anyway you look at it...

My boat was likely to sink or burn from dumb stuff the PO did.

His over propping has done nothing in nearly 2000 hours and 6000 miles...

So....if a boat buyer is the least bit smart and the surveyor the least bit good......is over propping an issue compared to all else boating?

Don't buy a used boat if you can't absorb what you are getting into.
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Old 01-18-2015, 06:50 PM   #3
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2000hrs for 6000miles ! unlikely over propping is a problem at 3nm/h.
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Old 01-18-2015, 06:54 PM   #4
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2000hrs for 6000miles ! unlikely over propping is a problem at 3nm/h.
Exactly....not directly related...just letting people know that depending on a lot of factors...over propping is just one of many things to consider...not necessarily fear.
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Old 01-18-2015, 07:09 PM   #5
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Don't buy a used boat if you can't absorb what you are getting into.[/QUOTE]

Good advise but some used boats take more absorbing than others. If you find poor wiring or plumbing or structural issues that have not yet triggered a problem they can be fixed(absorbed) , but internal motor damage that is already done but not yet fully destructive is harder to see. The WOT sea trial test is a simple indicator of how the engine was set up to run not a guarantee of proper use but helpful. There is also the cost of a new motor not a simple quick fix so this is not an area you want to do too much absorbing on a used boat. If there are two similar boats for sale with prices close and one has questions raised at survey possibly related to DIYS over propping which boat should the prudent buyer pick? Yes I know boaters are not always prudent.
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Old 01-18-2015, 07:14 PM   #6
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Seriously?

I had no more idea that my engine on my trawler was OK even though over propped than I did with my 3208Ts on my sportfish that weren't but had 3000 hrs on them.

You look for the bigger picture...the details while they sometimes seem important aren't always the whole story. Never bought a bad used engine because of the "big" picture...not one determining factor such as WOT.

You never can be 100% sure no matter what a sea trial says.
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Old 01-18-2015, 07:46 PM   #7
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The stupid thing about over propping is that there's almost no downside to doing it right.

All engine manufacturers recommend propping to rated rpm. One needs to toss out the sage advice of a lot of really smart people .. the smartest people in the world in this respect to propping or establishing a load for the engine.
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Old 01-18-2015, 08:28 PM   #8
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I see over-propping as a cheap way to get better economy or noise levels out of a boat when the current engine/gearbox/prop/hull doesn't match your needs. Maybe a good idea in some cases. But I'd keep the old prop(s) to bolt on at resale time.

A manufacturer doing it on a new build doesn't make sense.
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Old 01-18-2015, 09:54 PM   #9
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[
A manufacturer doing it on a new build doesn't make sense.[/QUOTE]


I just read somewhere that GH boats does it and has got according to what was printed approval of engine manufacturer. Of course GH did some research and testing prior to making the prop choices. And many builders for the sake of speed either over prop or prop on the edge of danger. There are many boats that sell because of a few extra knots not a trawler thing but very popular with the general boating public so lots of competition for those extra knots.
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Old 01-18-2015, 10:17 PM   #10
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Willard over propped 250rpm on the 30' models. Lots of other builders did it too ... it was "popular" in the 70s. That dosn't make it right though.
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Old 01-19-2015, 12:17 AM   #11
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Really enjoy when the subject comes up. Our last boat was over propped (Tenacious) to the extent that the 2800 rated RPM WOT was never in contention. More like 2400 RPM WOT and then the black smoke was heavy. We ran the engine at 1650-1700 RPM and after a 12 hour run tied to the dock, there always was a "smudge of gray exhaust".

For 13 years we ran it that way and the PO who installed the engine in the late 70's ran the boat with the same wheel for near 20 years.
We are as we have mentioned in the process of changing our our Perkins 4-154 fir a Perkins 4-236. According to what we can establish there were 18 hulls of this model Marben constructed. Each owner chose his power plant. It was about even as near as we can tell, half for this Perkins 4-154 and half with either the Perkins 4-236 or the Ford 80 hp four cylinder.
The 4-154 utilizes a 3:1 gear with a 22x16 wheel. According to the Vicprop formula this is about right on the mark. When we change out to the 4-236 and 2:1 gear the Vicprop calls for a 21x14.
As the Perkins 4-154 with the 3:1 turns WOT of 3000 RPM the wheel sizing is correct. This engine is rated at 58 hp. The Perkins 4-236 is 85hp. We are of the opinion that the success of the over prop on the Tenacious (70 hp at 2800 RPM) running a wheel of 21:x15 (Over propping) for so many years reflects that a similar over propping on the Slo~Belle will not becoming the horrid projection projected as "What might be".

So the project will be a 4-236 with a 2:1 gear turning a 22x16 wheel. How does that compare with the current engine. We run the 4-154 at 2400 RPM turning 800 RPM to obtain hull speed of near 7 knots (6.9 by formula). Using the same wheel and turning at 1600 RPM results in the same results. At that setting we still retain 800 RPM reserve off the 2500 rated WOT less the results of over propping when we establish that limit.

Using the former boat results one can anticipate a similar level of margin between Factory and over-prop RPM.

Awaiting the shop schedule to haul out and proceed.

We will remove approximately 450/500 # of lead ingot ballast due to the additional 500 plus additional # the 4-236 weighs over the 4-154. About the same foot print measurement wise just more #s.


We are seeking (1) updated engine model for parts availability (1960's model vs 2003 engine) and high engine hours on the 4-154
(2) Fuel burn: With the 4-154 at 2400 RPM we are near 2 gallons per hour. all indications will reflect a lesser burn at 1600 with the 4-236.
(3)quite. While the 4-154 is not loud in terms of cabin noise, the difference between 2100 RPM and 2400 is surprisingly different. On current boats with the 4-236 at 1600 RPM equals the level of the 2100 scale
(4) Human age! Not that many good years ahead. Now is the time, replacing the hot water tank and fridge as both are original l978 while the engine space is vacant Something to be said about quality of the times.

More power than required? Sure by formula this is true, no argument. Over all satisfaction weighs in as a compromise. We shall see
Al

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Old 01-19-2015, 12:57 AM   #12
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The "Smudge of gray smoke" was that left on the hull after the long run. Came off with a brush and Dutch powder. AMJ
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Old 01-19-2015, 01:39 AM   #13
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Quote:
Originally Posted by Al View Post
Really enjoy when the subject comes up. Our last boat was over propped (Tenacious) to the extent that the 2800 rated RPM WOT was never in contention. More like 2400 RPM WOT and then the black smoke was heavy. We ran the engine at 1650-1700 RPM and after a 12 hour run tied to the dock, there always was a "smudge of gray exhaust".

For 13 years we ran it that way and the PO who installed the engine in the late 70's ran the boat with the same wheel for near 20 years.
We are as we have mentioned in the process of changing our our Perkins 4-154 fir a Perkins 4-236. According to what we can establish there were 18 hulls of this model Marben constructed. Each owner chose his power plant. It was about even as near as we can tell, half for this Perkins 4-154 and half with either the Perkins 4-236 or the Ford 80 hp four cylinder.
The 4-154 utilizes a 3:1 gear with a 22x16 wheel. According to the Vicprop formula this is about right on the mark. When we change out to the 4-236 and 2:1 gear the Vicprop calls for a 21x14.
As the Perkins 4-154 with the 3:1 turns WOT of 3000 RPM the wheel sizing is correct. This engine is rated at 58 hp. The Perkins 4-236 is 85hp. We are of the opinion that the success of the over prop on the Tenacious (70 hp at 2800 RPM) running a wheel of 21:x15 (Over propping) for so many years reflects that a similar over propping on the Slo~Belle will not becoming the horrid projection projected as "What might be".

So the project will be a 4-236 with a 2:1 gear turning a 22x16 wheel. How does that compare with the current engine. We run the 4-154 at 2400 RPM turning 800 RPM to obtain hull speed of near 7 knots (6.9 by formula). Using the same wheel and turning at 1600 RPM results in the same results. At that setting we still retain 800 RPM reserve off the 2500 rated WOT less the results of over propping when we establish that limit.

Using the former boat results one can anticipate a similar level of margin between Factory and over-prop RPM.

Awaiting the shop schedule to haul out and proceed.

We will remove approximately 450/500 # of lead ingot ballast due to the additional 500 plus additional # the 4-236 weighs over the 4-154. About the same foot print measurement wise just more #s.


We are seeking (1) updated engine model for parts availability (1960's model vs 2003 engine) and high engine hours on the 4-154
(2) Fuel burn: With the 4-154 at 2400 RPM we are near 2 gallons per hour. all indications will reflect a lesser burn at 1600 with the 4-236.
(3)quite. While the 4-154 is not loud in terms of cabin noise, the difference between 2100 RPM and 2400 is surprisingly different. On current boats with the 4-236 at 1600 RPM equals the level of the 2100 scale
(4) Human age! Not that many good years ahead. Now is the time, replacing the hot water tank and fridge as both are original l978 while the engine space is vacant Something to be said about quality of the times.

More power than required? Sure by formula this is true, no argument. Over all satisfaction weighs in as a compromise. We shall see
Al

Of course I talk to myself, sometimes I need expert advice.
I am not saying he is wrong nor right , but an example of DIYS re- engineering with little or no real testing or science. That the older motor survived Over propping is no surprise many heavy iron engines had enough excess tolerance to do so. The newer the engine the less likely the same out come Also not all engines that experience excessive stress will fail only some will. Quoting the results of a single engine or a few would be little consolation to the few who have the failure. Its a little like the 80 year old smoker who assures people that smoking is harmless look he has done it all his life. Or the person who at 80 assures me that a bottle of gin a day is harmless because he is healthy and done it all his adult life. This issue will not be settled by back and forth anecdotal examples and probably not at all since the real experts , engine manufacturers, have little to gain by wading in to this debate. Just saying the likelihood of more DIYS tinkering in this aspect of boating may raise some interesting questions when some of these boats come on the used market. Would insurance companies take notice of the heavy smoker and the drinker? I wonder what they would think about DIYS over propping if they where aware?
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Old 01-19-2015, 04:54 AM   #14
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All Grand Banks boats back in the "low power" years when most of them were powered by one or two FL120s or similarly rated engines were deliberately over-propped an inch or two by the manufacturer. It was beneficial then, but I believe the practice was dropped when more powerful engines began going into the boats.

Our boat, from the first batch of fiberglass GBs made, was over-propped when delivered. A previous owner changed the original three-bladed props to four blade props which were over-pitched by the same amount as the originals. We run the boat pretty conservatively, so the over-pitching gave a bit more speed per given rpm without overtaxing the engines.

When we had the props completely reworked some years ago, the prop shop re-pitched the props down to give us max rated rpm at WOT. We go a wee bit slower for a given rpm than we used to, but the engines aren't working quite as hard as evidenced by the EGT gauges.
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Old 01-19-2015, 12:19 PM   #15
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Marin's statement particularly the last sentence is important. EGT readings are the key. Boats with adjustable pitch props are nothing new and almost all were run with EGT information used to determine RPM and pitch for safe efficient running. I would hope that people playing with over propping would at least use EGT and understand how to use it.
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Old 01-19-2015, 02:20 PM   #16
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For a single, over propping means much better low-speed maneuvering. I like being able to do that without adding throttle. Our GB32 was over-propped all its life, was still on its original engine when it was sold and my buyer ran her for 6 years like that; she's now for sale again, original engine.

Maybe with the new engines whose primary purpose is not to pollute so they run under much more rigid conditions, over-propping is not a good idea, but I understood that propping such that the engine is at max torque while you were at max cruise/hull speed was the ticket.
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Old 01-19-2015, 03:00 PM   #17
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Combining hull speed myth with over propping is where trouble begins.
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Old 01-19-2015, 05:18 PM   #18
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The more expensive boats I sell almost always have an engine surveyor and they always make a big deal about reaching top design RPM. They say how do you know that the engine is working properly if it will not get to the correct RPM. Is it the prop(s) or is it turbo charger, dirty fuel, bad injectors?
If you decide to over prop your boat, save the old prop to use when you put the boat on the market in the future.
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Old 01-19-2015, 06:51 PM   #19
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The more expensive boats I sell almost always have an engine surveyor and they always make a big deal about reaching top design RPM. They say how do you know that the engine is working properly if it will not get to the correct RPM. Is it the prop(s) or is it turbo charger, dirty fuel, bad injectors?
If you decide to over prop your boat, save the old prop to use when you put the boat on the market in the future.

So the buyer wont know how the motor is running unless it can pass a WOT testing. What about the guy selling the boat. If he cant and does not do regular WOT testing is he not missing something that might need a stich in time??
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Old 01-19-2015, 06:57 PM   #20
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Why does a couple hundred rpm seem like such a mystery on relatively low performance engines?

I don't think I have ever heard anyone suggest over propping high performance diesels in a go fast sportfish.

If the big deal is always about some specific engine being overpropped...then be specific....most people did using over propping as far as I can tell are usually discussing old iron .

I knew when every lawnmower I ever owned was cutting well or not...yet I never balanced the blade, cleaned the deck and performed a WOT test on any Briggs and Stratton.

Yet I always had nice lawns....
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