Docking question.

Nomad Willy said:

Steve K,
What’s the reason for needing to “achieve hull speed”?

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no reason to achieve it. we know these boats being discussed the GB36 is 8Knots so it seems if I ask what RPM gets you there with a single compared to my twins we have a point of reference for a comment of underpowered.

Mine back to starboard and side door is on starboard making thing easier. Except when you need to dock port side lol.
Anyway everything is a matter of learning, getting used to it, and improve skills.

L

The OP, Circumnavigator, wrote: "Question. Assuming that the GB36 backs to port -- most single screw boats do -- I don't understand their putting the only saloon door on the starboard side."

The door opening onto the side deck is on the starboard side because the helm station is there. That's only my surmise, but it makes sense, because crossing the salon en route to the door leading out onto the deck can be awkward.

As to the direction of the stern's swing in reverse, my experience running a 1988 GB 36 Europa with a single Cat 3208N (210 hp) was that it backed to starboard. But it wasn't dramatic, and really she could be made to back either way with a little momentum.

I found the 36' a wonderful boat and easy to singlehand. The 3208 had enough oomph to gather way quickly, scrub-off speed when necessary, and kick the stern around as you pleased with a burst of throttle and full rudder. That starboard door next to the helm put you close by to handle lines around the dock or in a lock. A later addition of a bow thruster tamed her completely.

Soo-Valley said:

I too have wondered what the usable differences are between a single and twin Lehman 120. To hear a single is underpowered makes me ask at what RPM does a single operate at to achieve hull speed of 8 Knots? My twins run at 1650 each for 8-9. Underpowered should mean unable to achieve hull speed?

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A single naturally-aspirated 80-HP engine should easily achieve hull speed on something-30-foot motorboat. (Works for my 17-ton, 35-footer which achieves hull speed 200 RPM [75% power] less than maximum although rarely exceeded 600 [30% power] less to achieve an economical one knot below hull speed.) Horsepower of 240 is overkill.

markpierce said:

A single naturally-aspirated 80-HP engine should easily achieve hull speed on something-30-foot motorboat. (Works for my 17-ton, 35-footer which achieves hull speed 200 RPM [75% power] less than maximum although rarely exceeded 600 [30% power] less to achieve an economical one knot below hull speed.) Horsepower of 240 is overkill.

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Thanks, I did not ask what engine HP, but the question was with same boat with same FL120 single v. same FL120 twins.
It was a FL 120 question on a GB36 since WOT is 2400 on 120. IF twins push at hull speed at 1650, what rpm does it take for the single to push at hull speed of 8 knots
It would be simpler if someone with a single 120FL would pipe in with the answer

It doesn't matter which way the engine turns, its the prop which determines the way she will favor when backing. Right hand props back to port,left hand props back to starboard. Many modern gear boxes (ubiquitous Twin Disc 502 etc) can spin either way and can use a RH or LH wheel w is designed this way without modification.

I'll join the chorus here.
My Grand Banks 32 with a single 139hp American Diesel (last non-turbo edition of the Ford Lehman) turns a left-hand prop and backs strongly to starboard. I have had a long learning curve after a lifetime of sailboats that had RH props and reliably backed to port.

-- Tom Dove

36 Grand Banks. Single Lehman 135. Left hand wheel backs strongly to starboard. I use it to my advantage.
1800 RPM pushes it a 7.5 knots towing an inflatable with motor......slack water.

Have you already sold Fintry? She’s a beauty, if there’s a link to sale info, Id be interested in looking.

You can change the rotation in most modern transmissions. Hydraulic transmissions are basically a pump and a motor. Direction is controlled by the valve.

My Mainship has a right turning prop and backs to starboard. It's VERY easy to control, overall. Helm on starboard with only a starboard door.



I thought it would be hard so I got a left turning prop and tried it. My ZF Hurth transmission handles the prop turning either way at any RPM, and changing the rotation with the Glendinning controls is not hard. However, it didn't make that much difference so I went back to the right prop.


In reverse, I can control the direction of the stern with the wheel... IF I go slow and occasionally coast a bit. The prop effect is much more pronounced with a goose of power, so that is used to my advantage.



Regardless of where the stern is, if I get a center cleat spring line on, I'm home free... just a matter of slowing working the boat up to the dock, and just leave in gear to get the rest of the lines. (wheel to port for a starboard tie, which is 95% of the time).



Now, add the stern thruster and makes it pretty easy.


I still have trouble backing into a slip with a current or wind. To counter act this, I've thought of adjusting the rudder for more swing, which Ted suggested I think about. But, that happens so rarely, I've put that project on the back burner.


Also, would have trouble single handling a port tie with a wind pushing me away.

psneeld said:

Anyone know of a single Ford Lehman (left hand engine) with a Borg Warner tranny that didn't back to starboard?

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That's what I've got, and I back to starboard all day long.

Yes, but the question was answered best that BW trannys turn either way and as long as you got the right prop...no big deal.

Just have to adapt as the capt.

Docking

Caballero II said:

That's what I've got, and I back to starboard all day long.

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I have a FL 120 and a BW xmission. My boat backs to port.

weird, mine backs up straight. Must be the twin counter rotating screws.

Bryant said:

I have a FL 120 and a BW xmission. My boat backs to port.

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Now that's weird to me, unless it's because of the previously mentioned BW transmission can turn either way. I'd love to hear about that .

Docking

Caballero II said:

Now that's weird to me, unless it's because of the previously mentioned BW transmission can turn either way. I'd love to hear about that .

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I’m not sure of how my transmission turns, other than performance on the water. In forward my stern goes to starboard. In reverse it goes to port.

For the BW, if it's a CR2 trans, it can be set up to spin the output either direction regardless of engine rotation. For a standard 72C, they rotate same as engine unless it's a 1.91:1 reduction, then it rotates opposite of engine.