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Old 04-14-2013, 01:10 PM   #1
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HELP! My boat only goes 5 knots

Hello all,

I have done some work on my 34' CHB Tri-Cabin and now she can't get out of her own way. When I bought the boat in Ventura Ca, sailed her down to MDR, Ca I was able to maintain 8+ knots at 1850ish RPM. Since then I have removed the Teak decks, fiber glassed and non-skidthem. I had a diesel run-away which required a complete rebuild of the engine and the injection pump. I replaced the rotten fuel tanks with Polyethylene cells in the middle of the approximate old location, but reduced capacity by half. Repalced two group 27 batteries with 4 deep cycle tall 6 volt batteries in the same location just in front of the engine.

No other major structural changes other than significant cosmetic upgrades like wall laminate, plumbing, paint, varnish, electronics and new heads.

Boat 34' CHB Tri-Cabin
120 HP Lehman
2:1 Paragon Transmission
23" 17 Pitch LH Prop - Tuned by Wilmington Prop in Wilmington Ca

Conditions:
No Load Engine Speed - 2800 RPM
Load Engine Speed - 2050 RPM
Heavy Cavitation
Hut Tub Like white water at the stern
Top boat speed of 5.2 KPH
Easy steering to the Starboard
Incredible difficultly steering to Port
Boat has a significant plowing issue when under power

Solutions tried thus far:
Swapped props -
22/18 4 Blade - picked up .2 of a knot and reduced cavitation very slightly steering issue unchanged
24/13 3 Blade - picked up .4 of a knot and reduced cavitation more but clearly not enough, steering still not correct
23/15 3 Blade - picked up .2 of a knot and reduced cavitation very slightly steering issue unchanged

Reaching out to Trawler community for experiences, solutions or suggested boat mechanics in southern Ca area.
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Old 04-14-2013, 01:24 PM   #2
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If you could get 8 knots before the alterations and eliminate all cosmetic ones that don't affect speed, to me that leaves the fuel tank change out. Could you have a blockage or restriction preventing enough fuel reaching the engine or is the line or filter plugged? I think you should get more than 2050 rpm WOT. Fuel??
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Old 04-14-2013, 01:28 PM   #3
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Boatdiesel.com A few bucks to join but you will probably get better answers there.

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Old 04-14-2013, 01:36 PM   #4
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If your turning the same RPM and lots of cav. my guess would be growth of bottom/prop. But you changed props and would have noticed. Maybe Tachs -knot meters lying to you, or trans is slipping? Check oil in gear case, burnt or really dirty?
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Old 04-14-2013, 01:56 PM   #5
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I'm with La Bomba on this. I would try running the boat using a portable fuel tank hooked up to the inlet side of the on engine fuel filters just to rule out the new fuel tank and lines that could possibly be suffering from things like inadequate venting or a vacuum leak.
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Old 04-14-2013, 01:57 PM   #6
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Quote:
Boat has a significant plowing issue when under power
Can you describe this a bit more? Is the boat floating on her designed waterline at the dock?

And if you tie the boat to the dock, put it in forward and rev the engine, what RPM can you reach?

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Old 04-14-2013, 02:48 PM   #7
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Island Eagle,

She sits at a similar water line to a another CHB in my marina. And when I throttle up in the slip same issue, 2800 RPM no load and only 2050 load...
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Old 04-14-2013, 04:05 PM   #8
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Quote:
Originally Posted by patzfan4eva View Post
She sits at a similar water line to a another CHB in my marina. And when I throttle up in the slip same issue, 2800 RPM no load and only 2050 load...
So what exactly do you mean by "plowing"?

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Old 04-14-2013, 04:09 PM   #9
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The tail raises and the nose buries...
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Old 04-14-2013, 05:05 PM   #10
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Wow, you've given us a good one.
You're turning the prop faster (2050 RPM vs 1850 RPM) and the boat lost 3 knots.
Air getting to the prop, (ventilation) or cavitation (little vaccuum bubbles forming on the surface of the prop) could cause this. No idea why this would happen on your boat.

The boat is plowing as you go faster when displacement boats usually squat as they go faster. Could the stern be raising high enough to let air to the prop?

The boat doesn't want to turn left. That will keep you out of Nascar.

Badly adjusted trim tabs could cause all of this but I'd bet you don't have trim tabs on that boat.
I think I'd be looking for a trim problem at this point.
When you figure it out, please let us know.
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Old 04-14-2013, 05:24 PM   #11
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Did you change props or gearbox?

Could it be a LH prop running on a RH forward drive transmission in reverse?

Just a WAG.
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Old 04-14-2013, 05:48 PM   #12
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I've toying with the idea of the wrong direction prop on the shaft, but its a counterclockwise (the aft) spinning shaft with a LH prop.
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Old 04-14-2013, 06:14 PM   #13
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Quote:
Originally Posted by patzfan4eva View Post
I've toying with the idea of the wrong direction prop on the shaft, but its a counterclockwise (the aft) spinning shaft with a LH prop.
I thought of that as well. However, it does not explain the low RPM, in fact the RPM should be higher.

I would focus on the RPM issue first. Eliminate the fuel system as a variable, and just do it all at the dock. You should be able to achieve rated RPMs.

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Old 04-14-2013, 08:12 PM   #14
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Although it shouldn't affect RPM, have you moved CG forward with your new fuel tank install?

At what RPM did you achieve 7-8 knots before the changes?
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Old 04-14-2013, 09:06 PM   #15
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Around 1850 I was able to reach 8+ knots prior to change.
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Old 04-14-2013, 10:40 PM   #16
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If the loss of speed and steering problems started at the same time, my guess is something on the hull dragging on the starboard side. It would be worth a quick dive to check it out. Weed growth, hull damage and delamination, a giant blister opening up, dragging a net?
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Old 04-15-2013, 12:44 AM   #17
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In your original description you mention an over speed and rebuild. Do you think you actually getting the same power as before? Perhaps injector pump timing?...? However this would have nothing to do with the steering problem and the hot tub water.
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Old 04-15-2013, 01:56 AM   #18
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Bow thruster? And if so something caught in the tube?
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Old 04-15-2013, 02:14 AM   #19
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Who did the rebuild? Is the timing set correct? Giant squid attached to hull? As someone already said, join Boatdiesel. http://boatdiesel.com/index.cfm?FM=1 or call the folks at American Diesel. Good luck!
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Old 04-15-2013, 03:27 AM   #20
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This is a weird one. It is essentially the same vessel as mine, but in aft cabin form, and yes with clean bottom I can get 8 kn at about 1850rpm, and as all he has done to the boat is cosmetic and inside the vessel, it should not have altered running charactieristics at all, even a dirty hull would not cause anything but a slower speed. I am intrigued by this diesel runaway and the engine rebuild following that. We just had a discussion on another thread about how unlikly that is, and if it blew the engine, one wonders what was done and why, and was it done right..? The new tanks and less fuel load should hardly affect the trim enough to cause ploughing and cavitation, but sound slike it might have, and there is clearly soemthing separately wrong with the steering I would say...
I also wonder like someone else mentioned re slipping in the gearbox (transmission), especially as the rev's drops off a lot under load, but the speed is way down. I also agree fuel starvation could contribute to some of the problem, but not all, especially not the trim/cavitation issue.
It will be very interesting to find out what it is in the end.
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