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running a triple with two motors

Old 11-27-2012, 06:14 AM
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Default running a triple with two motors

We had an issue with the center motor and we decided not to run it until getting it checked out. But when we ran the two outside motors (with center trimmed up) we could only get to about 2700-3000 rpms before the motors would start cavitating. It's a 36 contender with f250s and we were full on fuel, so we definitely weren't on the light side. I got the boat last January...........so haven't tried it before. But I was hoping that two motors could at least get the boat on plane.

Any advice/experience appreciated - Dan
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Old 11-27-2012, 06:52 AM
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Default Stepped hull? right. I believe 2500RPM on a non stepped boat would be good

Originally Posted by dward View Post
We had an issue with the center motor and we decided not to run it until getting it checked out. But when we ran the two outside motors (with center trimmed up) we could only get to about 2700-3000 rpms before the motors would start cavitating. It's a 36 contender with f250s and we were full on fuel, so we definitely weren't on the light side. I got the boat last January...........so haven't tried it before. But I was hoping that two motors could at least get the boat on plane.

Any advice/experience appreciated - Dan
Trim all the way down as low as possible. The outboard engines are not grabbing deep water like the center. Maybe 5 inches difference. If stepped. the gain in speed could be causing a slow speed clean water effect. I know my friends sea vee 34 w trips planes easy even with full tanks on two engines. We had some early gear box problems that merc made good. But came in on 2 engines more then once. Very heavy boat also. with bottom paint.
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Old 11-27-2012, 07:00 AM
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It is not a good idea to run a triple powered boat on less than all three motors. If you do you are lugging the motors that are being used. That is, there is too much propeller pitch for just two out of three motors propelling the boat, when the motors were originally propped based on all three being operable.

This is operator abuse. Should one of the two motors fail, or be damaged, due to being overloaded are you willing to take the financial hit? Any such damage would not be a warrantable defect. There is no defective part. Something external to the engine caused the damage.
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Old 11-27-2012, 07:07 AM
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Originally Posted by jethro1 View Post
It is not a good idea to run a triple powered boat on less than all three motors. If you do you are lugging the motors that are being used. That is, there is too much propeller pitch for just two out of three motors propelling the boat, when the motors were originally propped based on all three being operable.

This is operator abuse. Should one of the two motors fail, or be damaged, due to being overloaded are you willing to take the financial hit? Any such damage would not be a warrantable defect. There is no defective part. Something external to the engine caused the damage.
No disrespect meant at all Jethro but isn't that the point of redundancy? Being able to continue to operate with less than all available engines.

I understand the argument to go back to port at idle speed to avoid damage to the remaining motors but that is not always practical.

In my industry we say that "one engine belongs to the company and the other belongs to me!" Meaning that if one fails the other might be used to its fullest extent and perhaps a bit beyond to protect human life. IE if one fails the other may be purposefully sacrificed to ensure a safe landing.(apples to oranges comparison but amusing nonetheless!)
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Old 11-27-2012, 07:20 AM
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[quote=jethro1;5129738]It is not a good idea to run a triple powered boat on less than all three motors. If you do you are lugging the motors that are being used. That is, there is too much propeller pitch for just two out of three motors propelling the boat, when the motors were originally propped based on all three being operable.

This is operator abuse. Should one of the two motors fail, or be damaged, due to being overloaded are you willing to take the financial hit? Any such damage would not be a warrantable defect. There is no defective part. Something external to the engine caused the damage.[/quo

why would you buy trips other wise? ie trip F250's over twin 350's?
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Old 11-27-2012, 07:32 AM
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When I had OX 250's on my 36 C, it did the same thing- I had to ease in the throttle, with some down tab, and tilt full in- otherwise she cavitated. Once she was up, she actually did fine.

After the re-power to Vrods, she would pop right up on plane-

Randy
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Old 11-27-2012, 07:35 AM
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Default X2 I do not believe you should go much over planing tho.

[quote=ono loco;5129801]
Originally Posted by jethro1 View Post
It is not a good idea to run a triple powered boat on less than all three motors. If you do you are lugging the motors that are being used. That is, there is too much propeller pitch for just two out of three motors propelling the boat, when the motors were originally propped based on all three being operable.

This is operator abuse. Should one of the two motors fail, or be damaged, due to being overloaded are you willing to take the financial hit? Any such damage would not be a warrantable defect. There is no defective part. Something external to the engine caused the damage.[/quo

why would you buy trips other wise? ie trip F250's over twin 350's?
I think once its planed off and cruising it should be good. if not then why trips? There are boats out there with twins that are not being abused because their owners decided to go twins over trips? Yes full fuel is a problem. OP never came back to let us know if its a stepped hull?
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Old 11-27-2012, 09:34 AM
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There are boats out there with twins that are not being abused because their owners decided to go twins over trips?
I guarantee you their prop pitch isn't the same though.
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Old 11-27-2012, 10:08 AM
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Trim center motor all the way down, it helps push the bow down. Also run your tabs all the way down and move as much weight up front. Then let her eat. Once on plane start to back off the tabs. That is the point of having trips. That boat should hit about 40 to 45 mph running on two. I had the same problem this summer after losing a lower unit on the center. If you dont tab and trim down they will not bite and start to cavitate.
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Old 11-27-2012, 11:06 AM
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Thanks for the responses, and sorry for the delay in responding, I've been in meetings all morning. It's an 06 Contender CC with 06 F250s, and it is not stepped...............As I make long runs to the Tortugas with the boat, I was under the assumption that if you lose a motor a hundred miles from home, the purpose of having triples is that two will get you back at a reasonable pace.

I did have the outside (running) motors trimmed all the way down, and the center (non-running) trimmed all the way up (out of water), but I didn't do anything with the tabs. I had the center motor trimmed all the way up thinking it would reduce drag, but the post above recommends it being down helps??

I agree with why get triples if two won't get you home??

Thanks
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Old 11-27-2012, 11:14 AM
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Tabs certainly have to be down. Get the nose down and get the boat moving. Then retab up as the boat gets movin. Heck, on my sport fisher it's tabs down, wind up the engines, 16 knots back em off, 23 knots a tad more, 26 knots find the sweet spot and sit back.
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Old 11-27-2012, 11:23 AM
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If running with less than all motors causes the running motor(s) to lug (work harder), the operating temp. will creep up.
As long as you do not overheat, all should be good to go.
Right ?
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Old 11-27-2012, 11:50 AM
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Engines are made to run. How many 36 foot center consoles are out there with twins????

Quite a few.

Tab down and roll into the throttle, should pop up. I do question whether your propped correctly overall if it cavitates that easily.
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Old 11-27-2012, 12:02 PM
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Is there someone with triple anythings that can run all three of them at WOT (record the engine RPM) and then shut down one of the three to see what the WOT RPM with two of the three running is?

I am guessing that with two of the three running the motors won't get into the WOT RPM that the engine makers specify. But, it is just a guess. It would be good to know.
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Old 11-27-2012, 12:05 PM
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[quote=ono loco;5129801]
Originally Posted by jethro1 View Post
It is not a good idea to run a triple powered boat on less than all three motors. If you do you are lugging the motors that are being used. That is, there is too much propeller pitch for just two out of three motors propelling the boat, when the motors were originally propped based on all three being operable.

This is operator abuse. Should one of the two motors fail, or be damaged, due to being overloaded are you willing to take the financial hit? Any such damage would not be a warrantable defect. There is no defective part. Something external to the engine caused the damage.[/quo

why would you buy trips other wise? ie trip F250's over twin 350's?
Beats the heck out of me.
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Old 11-27-2012, 12:10 PM
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Regarding the two versus three engine scenario, whatever props are installed are based on the WOT RPM with all of them turning. If one stops turning (one of two or one of three) then the others are automatically overpropped. By exactly how much is unknown.

I doubt that anyone would buy three motors versus two on the basis that they can run back home at cruise speeds with one of three failed. On the other hand, folks do some strange stuff.
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Old 11-27-2012, 12:16 PM
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Originally Posted by stl32 View Post
Trim center motor all the way down, it helps push the bow down. Also run your tabs all the way down and move as much weight up front. Then let her eat. Once on plane start to back off the tabs. That is the point of having trips. That boat should hit about 40 to 45 mph running on two. I had the same problem this summer after losing a lower unit on the center. If you dont tab and trim down they will not bite and start to cavitate.
^X2


The reason for trips is I can run home on twins! If you have the older 36, it is most likely propped wrong.
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Old 11-27-2012, 01:19 PM
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I would trim the engines as you have, with full trim tabs down to start with--the "lift" of the center engines not running is minimal, but the drag is considerable. If the outboards are caveating with the tabs full down, and the outside engines full down, trim the outside engines up slightly. Agree that the boat should plane, but will not reach desired WOT. Backing off on the engines to in the mid to high 4,000 range should allow them to safely get the boat home on a plane, once up.
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Old 11-27-2012, 03:26 PM
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Your probably running yamaha SWS 23 pitch propellers.
Depending on how you load the boat, you may be a little overpropped to start with.

a set of Revolution 4's or Powertech OFS4'swould probably push you up on plane without ventilating the props. even while running on 2 motors.

Whether its a good idea for the motors, or warranty or whatever, that can be argued either way.

But I think you could get it on plane with a set of 4 blades.
You'd probably like the way the boat ran with them normally as well.

Last edited by ken2; 11-27-2012 at 03:57 PM.
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Old 11-27-2012, 03:30 PM
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Originally Posted by jethro1 View Post
I doubt that anyone would buy three motors versus two on the basis that they can run back home at cruise speeds with one of three failed. On the other hand, folks do some strange stuff.
Thats one of the primary reasons most people go with trips, for example, a 34 YF runs GREAT with twin F350s, yet you dont hardly ever see this set up. For guys fishing 50-100 miles one way, running in on two at 40 beats running on one at 8!!
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