Marinette Boat Forum

There have been past side comments on this topic, but I start a new thread to address this topic, as it doesn't seem to be clear on the best approach, and it is hard to locate comments when they are in other topic's posts.

Problem: a boat needs to go a long distance on limited fuel. We have the option of running both motors at lower rpm's, and don't try to plane off the hull. Like around 1500 or a bit more. Fuel economy when on plane seems to be worse? It might be questionable, as the hull is planed off and has less drag. Some have posted mpg in assorted posts and there seems to be a big range.

Or run on one motor? This approach brings up the subject of whether to leave the velvet drive in gear, (to stop the prop from rotating, and saving wear on the drive). clamping the shaft to stop rotating ( to save stress on the transmission), or putting the drive in neutral (leaving the prop spin, less drag, ….but what does that do the drive?)

So I ask for those who have tried these options, and what you concluded.

Thanks in advance for you input!
Capn Gary

32' FB Milton, Fl

I spend a lot of time running on one engine for fishing. Two engines would be too fast. If you have a Velvet drive it doesn't matter what you do with the shifter when the engine is not running, nothing will happen. Just like an auto transmission in a car, sit there with the engine off and you can move the shifter and you just move the shifter. Putting the shifter for the velvet drive in gear will not stop the prop from turning. The Velvet drive is just fine free wheeling and if you do clamp the propeller shaft so it doesn't turn you will just cause more drag and slow the boat.
There are many variables, the weight, loading, trim, wind, current, waves, cleanliness of the bottom, even who is steering. In a nutshell I think you will find a most economical cruise at a slow speed and one at a higher speed. Higher speed should be just enough power to get you on plane, then you should be able to back off the power a little bit. This is where the load you have and how it is loaded and how you have the trim tabs set will make a big difference. Slow speed should be one engine just above an idle or thereabouts. But if you are going into the wind or current, or with it will change everything. Going slow into a current you may be standing still or going backwards. Going with the current, absolutely the most efficient thing to do is shut them both down and burn zero gas just drifting. Things you can do are keep the engines tuned up so they run well, get rid of excess weight to haul around and load the boat correctly. ( for me that is put all the weight I can up front )

And don't forget a very significant fuel burn item: a clean bottom. Shmootz costs

Great topic! I’ve asked a few times for someone with a floscan system to post a fuel usage chart for us. Hopefully you floscan guys can help us out this spring. I have a 29 and I use one engine most of the time. About 1700 rpms gets me 7mph. I usually just enjoy a slow cruise for an hour then set anchor for the day in a cove. Save lots of money on one engine if you’re not in a hurry. People sail around the world at 7mph/knots...that is unbelievable to me. That has to be very boring

Great topic.
I have NOT ran our 39 on one engine yet. I am investigating the same thing for future longer river trips. Here are my thoughts WITHOUT concrete details.

With respect to fuel efficiency, based on my experience with a few different boat hulls, barely over HULL speed (making no wake) will likely be the most efficient and then "just on plane" will be the next more efficient rate. I would guess that keeping the four barrel from kicking in is the basic objective on plane. I still don't know for sure where my 39 planes well at. At close to hull speed, there should be savings on one engine. I have a friend that has travelled across Lake Huron 350 miles every summer for almost 20 year and runs mostly on one engine. It is a 38 Bayliner with small diesels so it is not exactly out the same as the Big M world. Also running at hull speed may not fit into ones time schedule.

I called Kalamazoo Marine Gear based on a reference from a long time Crusader/ Velvet drive boater regarding locking or free spinning the tranny.
Craig at this shop has decades of experience with the Borg Warner trannys and recommended locking the shaft if going longer distances at speeds greater than 7-8 knots. This was based on his logic that the transmission turning without any lubrication pumping oil in it was not good from a mechanical perspective. He did say that some internal parts were partially submerged in oil - which would help while the pump is not running. If going hull speed, It MIGHT be just fine for the prop to spin in his opinion. He said that most of the fisherman trolling on one engine that he knows lock the tranny but there are many that don't. He also said that he thought that Borg Warner stopped offering recommendations about this years ago.

I hope to install fuel monitoring senders in the next couple of years. There are some old sending units on my engines but I'm told that they are not supported any longer.

I spun the ring gear off my port engine flywheel two hours into a two day trip the day I picked up my new to me river cruiser houseboat. Not only first day with boat, first time piloting any boat (first boat was a 14' aluminum Grumman canoe). Rest of trip was a little hairball to say the least. Great learning experience and no harm done as far as I can tell.

Crazy as it sounds, everything I know about boats I learned from the internet and drunk people. So far so good. Praying for a quick thaw in upstate NY.