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Old 02-28-2013, 10:41 AM   #1
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Marine Trader 34DC Cruising Speed

This may have been asked before, but using the search on the forum, I cant find anything on it.
Google has returned a few results but they vary, so let's try it here.

I pick up our 1979 Marine Trader 34DC in April.

I am starting to think about the details of the 330nm passage to get the boat from its current location to home. I will do it in one go if the weather holds. I want to establish a realistic boat speed for the passage that has reasonable fuel consumption.

During the survey and sea trials, I noticed the boat pushed out very little bow wave up to about 6 to 7 knots. After which she really dug in and started to move a lot of water as she reached 9 to 10 knots.

My questions is not about the exact fuel consumption calculations because every boat is engineered differently.

What I want to know is what speed does the boat cruise efficiently at with relation to the hull design and water line length. As a displacement boat goes faster, she digs in and pushes out more water, so the harder it works to do it, and the more fuel she consumes. Yes, yes i know, there are loads of other factors for the actual consumption based on engineering etc, but the displacement of more water is IMHO and experience a primary reason for such a significant increase in consumption.

I hope those of you with MT34's understand what I am trying to establish and can give me a good estimate for my passage planning.

Cheers!
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Old 02-28-2013, 11:40 AM   #2
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Fully loaded for passage making, "Angelina" did about 2 gallons per hour at 1750 rpm which gave me 7.5 knots.
Usually 1750 rpm would move her at 8 knots but not when she is packed to the gills.
Anything more than that and you are just throwing away fuel and digging a bigger hole. You will not go any faster.
Good luck on your trip!
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Old 02-28-2013, 11:59 AM   #3
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Fully loaded for passage making, "Angelina" did about 2 gallons per hour at 1750 rpm which gave me 7.5 knots.
Usually 1750 rpm would move her at 8 knots but not when she is packed to the gills.
Anything more than that and you are just throwing away fuel and digging a bigger hole. You will not go any faster.
Good luck on your trip!
Thanks, very useful.
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Old 02-28-2013, 12:48 PM   #4
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Greetings,
Mr. sailtones. I have experienced EXACTLY what Mr. alormaria has posted re: the MT 34 DC. In conversation with Mr. Bob Smith of AD many moons ago, he noted that 1750 RPM seemed to be the "sweet spot" for the 120 Lehman. I also found that Ms. Lehman "liked" 1250 RPM as well. Just coincidence that the tach' needle pointed to the 2 rivets at the top of the face of the Motorola at these 2 RPM's at about the 10:30 and 1:30 positions respectively. Can't remember the ground speed @ 1250 RPM though...
Keep in mind that not all 34 MT's use the same hull. Hope this helps
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Old 03-01-2013, 03:57 AM   #5
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Greetings,
Mr. sailtones. I have experienced EXACTLY what Mr. alormaria has posted re: the MT 34 DC. In conversation with Mr. Bob Smith of AD many moons ago, he noted that 1750 RPM seemed to be the "sweet spot" for the 120 Lehman. I also found that Ms. Lehman "liked" 1250 RPM as well. Just coincidence that the tach' needle pointed to the 2 rivets at the top of the face of the Motorola at these 2 RPM's at about the 10:30 and 1:30 positions respectively. Can't remember the ground speed @ 1250 RPM though...
Keep in mind that not all 34 MT's use the same hull. Hope this helps
Thanks Firefly.

It will be interesting to see how my MT actually performs with regards to fuel consumption. She has 2 x 130hp Volvo's!
On the sea trial she was doing 6/7ish knots with very low revs on both engines. Full revs on both engines put her over 10, but I imagine she would be super thirsty doing this. Unfortunately the previous owner passed away, so I cant ask him...

Thanks again.
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Old 03-01-2013, 05:30 AM   #6
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The normal CHEAP to operate speed for any displacement boat is from .9 to 1.1 times the SQ Root of the underway Length on the waterline , in Knots.

If you cruise at a higher speed by very little the fuel burn will easily doubble , "hull speed" the burn can triple.

The usual solution is to stay inshore where the charts are in lubber LAND miles so 5K becomes 6 mph. A 20% improvement.

In inshore cruising on the AICW it seems most common for folks to do about 60 stat miles per day.
Takes dedication in the fall to get underway early when the days are cool and short.
Pretty easy to run in the spring with longer days.
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Old 03-01-2013, 08:09 AM   #7
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On a recent trip where we did about 140nm in a day non-stop, with virtually no adverse current, we saw an average of 7.2kn @ 1750rpm, as others have stated, that seems to be the sweet spot. I would allow for a longer trip such as your planned delivery home trip, to only average 6.5kn, for really good fuel consumption, and the fact you will certainly meet some adverse current/tidal flows and some wind/weather on the nose.
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Old 03-01-2013, 08:22 AM   #8
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Greetings,
Mr. sailtones. Hmmm...twin Volvo's? Have NO idea at all. I based my comments on a single Lehman. Could be a bit cramped in the ER...no?
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Old 03-01-2013, 08:28 AM   #9
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Greetings,
Mr. sailtones. Hmmm...twin Volvo's? Have NO idea at all. I based my comments on a single Lehman. Could be a bit cramped in the ER...no?
Actually she is not to bad. A bit of a squeeze to get outboard of the engines. But I come from the sailboat world so in comparison, it is a dream!

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Old 03-01-2013, 08:40 AM   #10
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On a recent trip where we did about 140nm in a day non-stop, with virtually no adverse current, we saw an average of 7.2kn @ 1750rpm, as others have stated, that seems to be the sweet spot. I would allow for a longer trip such as your planned delivery home trip, to only average 6.5kn, for really good fuel consumption, and the fact you will certainly meet some adverse current/tidal flows and some wind/weather on the nose.
Thanks for the info Peter. Very useful.

Here is a little map of the trip, starting in Italy and ending in Montenegro. If anyone is interested......

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Old 03-01-2013, 09:57 AM   #11
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Thanks Firefly.

It will be interesting to see how my MT actually performs with regards to fuel consumption. She has 2 x 130hp Volvo's!
On the sea trial she was doing 6/7ish knots with very low revs on both engines. Full revs on both engines put her over 10, but I imagine she would be super thirsty doing this. Unfortunately the previous owner passed away, so I cant ask him...

Thanks again.
2 130 hp engines in an MT 34??? The previous owner probably died of suffocation. He was unable to breath he was going so fast!! You should be required to have head restraints or at least seat belts in something so overpowered!!!

Oh, the humanity....
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Old 03-01-2013, 10:44 AM   #12
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2 130 hp engines in an MT 34??? The previous owner probably died of suffocation. He was unable to breath he was going so fast!! You should be required to have head restraints or at least seat belts in something so overpowered!!!

Oh, the humanity....
LOL
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Old 09-18-2014, 08:45 AM   #13
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Cruising speed Marine Trader

I too acquired a Trawler. 34' Marine Trader twin engine SP130 Lehmans. From Ft. Walton Beach to Kemah Tx. 1600 - 1800 rpms @ 8-9 knots. Averaged 3-4 gph with the generator operating 80% of time.
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