CHB 34 cruising speed?

With a 120 FL what is the cruising speed of a chb 34? Can it cruise at 8kts? I’ve heard 7kts up to 11kts.
Thanks

Greetings,
Welcome aboard. We had a MT 34' with a 120 Lehman. The two "sweet spots" were 1250 RPM and 1750 RPM. Can't remember actual speed (7 kn @ 1750 perhaps?). I figured as long as the engine sounded happy it really didn't matter much what the speed was. A knot or two either way doesn't matter to me.

When a boat gets this close to FD the good cruising speed range is really quite small. A little under 7 to a bit over 7 is probably about right. However 6.5 wouldn’t be ridiculous and 7.5 would be fine for the trawler skipper only traveling short distances. 8 knots would be done only by those liking a big wake and not concerned about fuel burn.
So there’s not much “range” and as RT says it’s mostly a matter of the engine being at a speed (rpm) that is smoother than other speeds within the range.

Simple enough but higher speed SD hulls will have a wider range and make the choice of cruise speed more complicated. But the CHB is close to FD.

Grandbanks3642 said:

With a 120 FL what is the cruising speed of a chb 34? Can it cruise at 8kts? I’ve heard 7kts up to 11kts.
Thanks

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Depends on the engines. We had a
CHB 34 with twin Volvos, and cruised at 11 knots. With the single diesel, 7-8 sounds about right.

I have a Marine Trader 34 which is a very similar hull (if not identical) and it is powered with the Ford Lehman 120. Like RT Firefly said, the sweet spot is right around 1800 rpm and that produces 5 - 9 knots depending on the wind, sea state, and current. on a calm day with no current the 1880 rpms will get you 6.5 - 7 knots. You can push it harder but it yields almost nothing except burning a lot more fuel. If you can live with the speeds I listed then you may be happy with the boat. If not, look for a different boat with a different hull design and power configuration. We love ours - but we aren't getting anywhere quickly.

Our CHB 34 with a single 120 FL cruises best at around 1650 to 1700 RPM. If running late I'll push it to 1800 RPM. I have always used the philosophy that If I'm starting to lift the bow out of the water I'm burning more fuel then optimal. At 1650-1700 she runs at about 7 to 7.5 knots.

What's the waterline length?

-Chris

NWSeadog said:

Our CHB 34 with a single 120 FL cruises best at around 1650 to 1700 RPM. If running late I'll push it to 1800 RPM. I have always used the philosophy that If I'm starting to lift the bow out of the water I'm burning more fuel then optimal. At 1650-1700 she runs at about 7 to 7.5 knots.

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Re the bow rising ..
I usta thing that was hull speed. Far from it. On my Willard the bow starts rising at about 5 to 5.5 knots. That would give excellent economy but my hull speed is 7 knots. I cruise at 6.15.
At 1800rpm I wouldn’t say you’re pushing it .... unless you’re overpropped.
But I agree fully once you start climbing your wave you will be burning more. But every time you increase throttle you burn more. Even w no load at all.

I think the LWL on a CHB 34 is right at 30 feet, but don't quote me on that. If my numbers are right that would give a hull speed of 7.34 knots.

My probably misguided thought is that when I start lifting a 20,000 pound boat vertically instead of moving it forward I'm wasting energy that I could be using for moving forward. It is probably just a fluke that the nose on our boat starts climbing up at around that speed.

NWSeadog said:

Our CHB 34 with a single 120 FL cruises best at around 1650 to 1700 RPM. If running late I'll push it to 1800 RPM. I have always used the philosophy that If I'm starting to lift the bow out of the water I'm burning more fuel then optimal. At 1650-1700 she runs at about 7 to 7.5 knots.

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i must be under propped i have a 38 and i get 6.5 at 1800 or so .

NWSeadog said:

I think the LWL on a CHB 34 is right at 30 feet, but don't quote me on that. If my numbers are right that would give a hull speed of 7.34 knots.

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That calculation works, although I'd probably label that "maximum theoretical hull speed" versus just plain ol' "hull speed,"

Beebe suggests best fuel economy for that length at about 5.5-6.0 kts -- 1* or 1.1* SQRT(LWL).

-Chris