Trojan Boat Forum

I know this has been discussed in other forums, but I thought I would ask the Trojan community. What are the issue with running one engine at displacement speeds. Any issues with the Velvet Transmission or the shaft packings? Should you run in gear or free wheel it? If you switch back and forth, what is the maximum amount of time on one engine.

With fuel costs and gas guzzling motors, I've come to the conclusion that I will be running slow. I'd like to know if its safe and worth it to run one motor.

Opinions?

Great questions. I will be looking for some reasonable responses!

I don't do this with my Trojan..... As I think about it no reason why not.

I have done it on the President a number of times due to having one engine down. I have a velvet drive on it.
I have not seen any problems with the transmission nor the packing running for 6/8 hrs per day. (NOTE I use GFO dripless packing)
I found that I was running at almost the same speed when on one...... was I pushing too much water on 2? Was it because I was going down a river?

I did this for 2 seasons a few years back before I replaced a bad starboard engine. 1972 30' Flybridge Sea Raider. I had low oil pressure so I only used the starboard engine when maneuvering to or from my slip or a dock. While there is a considerable fuel savings, it's not half. My rpms were higher at hull speed than on two engines. All in all it worked fine as long as I used both to maneuver. I much prefer using both engines and being able to plane and travel faster....John

Todd:

I don't know what your actual hull speed is.

That is to say, running at your most efficient speed below plane may be a better answer to the problem.

Run that calculation then experiment on one vs. two engines, assuming its safe to freewheel with your specific gear.

Once you know the numbers, run your burn calculations for a given trip.

THEN run a COMPARISION of the calculations and factor in ONLY the DIFFERENCE in fuel cost/savings.

You may be surprised by the answer !

Here's a repost from earlier this year of the performance test and hull speed calculation completed by Ready123, BobCT and RWS.

Keep in mind, this is a Ten Meter Express with 6 cylinder diesel turbocharged/intercooled engines.

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Re: Short notice. Fri RWS get together in Punta Gorda?

Postby RWS » Sat Feb 02, 2013 10:41 am

An interesting and fun day on the water was enjoyed by Forum members BOBCT and READY123 aboard RWS 10 Meter Express.

Before departing the dock a through inspection took place of all machinery and user upgrades and modifications.

After a luncheon of build your own sandwiches and snacks, gourmet fresh caught shrimp and multiple dipping sauces (hot sauce and pussy sauce) supplied by Ready123 the group posed for photos (to be added later) and then went about the tasks of evalusting the vessel and taking some notes.

For the record here are the actual LOA numbers on the 10 Meter Express Cruiser:

hull length - bow to transom rubrail 33' 6"

hull length including bow pulpit 37' 8"

hull length from bow pulpit to swim platform 39' 3"

waterline length (observed) 29' 1"

According to the hull speed calculation - <SNIP> 1.34 times the square root of the waterline length is just a rough approximation of potential hull speed. It is good only for fairly heavy (nowadays) displacement hulls. But actual speed potential for every hull will be slightly or not so slightly different, as there are several other factors involved.

Beam has been mentioned, but is actually meaningless of itself. Key factors are length, weight (displacement), and form (the hull shape). The shape of any particular hull's resistance curve will vary with any of these factors. Beam is only important as it generally follows that narrow hulls are lighter, thus resistance lower and potential hull speed higher. <SNIP>

The hull speed calculation for this vessel ciphered out at 7.2 knots per hour.

That said the real world application for our own testing purposes is actually 6.5 knots/hour on testing day with no allowance for tide or winds.

With BOBCT at the helm, our observed speeds:

low cruise 20knots 3000 RPM

nice most used cruise with engines feeling light and "singing" 22.7 knots at 3300 RPM

high cruise at max reccomended cruise RPM 24.2 knots @ 3600 RPM

WOT speed was 27.1 knots at 4050 RPM

Watch this thread for more information to come including details on our 34 nautical mile adventure, on the Harbor and the Peace River including alligators, vultures, pink spoonbillshatburds and more, not to mention the dredging of the river.

to be continued

SAME BAT-TIME

SAME BAT-CHANNEL

RWS

Yes you can save fuel that way as long as your at hull speed and below . Just may sure your gear is rated to free wheel . Velvet drive 72 & 72 are as is the ZF 220 . If you have drip less shaft seals check with the manufacture . If you have drip less seals and a cross over for the water feed . you could back feed the non-running engine .

prowlersfish wrote:Yes you can save fuel that way as long as your at hull speed and below . Just may sure your gear is rated to free wheel . Velvet drive 72 & 72 are as is the ZF 220 . If you have drip less shaft seals check with the manufacture . If you have drip less seals and a cross over for the water feed . you could back feed the non-running engine .

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I have yet to tie mine together - but if/when I do I will be certain to include three maleron ball valves into the system as I would be concerned about dumping water back into the non running engine via the exhaust system and exhaust valves.

That would not be pretty.

RWS

I run on one engine all the time but I switch back and forth.

No problems.

my friends and i all run one motor in and out of the chanel, trolling fishing etc, no problems and big fuel savings, cheers

This is the statement that I received from Walter for the V-drives;

I can only answer for the V-Drive, not for the transmission. For the Walter V-Drive, it is better to lock the shaft so prevent the V-Drive from turning. However, if this is not possible, at LOW rpm and low hull speed it is generally okay for the V-Drive to free wheel, provided the V-Drive does not get too warm (if the engine is off the cooling water to the V-Drive may not be circulating). On an installation where scuppers are used to cool the V-Drive, this should not be a problem.

I'm not sure what Low hull speed is...

Todd,

What do you estimate your fuel burn per engine assuming your hull speed to be the same as mine at 6.5 knots?

Whatever it is your savings will certainly be less than 50%

I cut and pasted my detail data from 2002 with the 454 gas engines running quadrajets.

This shows a fuel burn of between 2 - 3 gph per engine at hull speed.

The 10 meter has a wide beam with the engines placed wider apart than on a typical 33' boat.

This forces a hard rudder angle with one dead engine.

Add to that the additional drag of the dead running gear.

Add to that the higher RPM of one prop required to run at a given speed vs. 2 props.

Lets figure high.

Assuming 3 gallons per engine per hour - six gallons per hour total fuel burn, and an efficiency loss of 20% (pick your own number, but I'd bet its closer to 40%)

six gallons at $4.00 gallon is $24 per hour.

Assuming the above, I'm burning 3 gallons per engine, or $12 per hour per engine.

So I can save $12 per hour less the efficiency loss of 25 % which equates to $3 resulting in a savings of $9.00 per hour at hull speed.

If you had flowscans - you could run a TRUE test to see how much more fuel one engine would burn vs. two at hull speed.

For me, I'd run hull speed for the savings, but would run both engines.

Here's the cut and pasted raw data from my vessel.

RWS

DETAIL ON THE CHART:

after change to 18x19 pitch by Coastal Prop Technology, Inc.
Carbs previously swapped port & stbd
carrying 202 gallons gasoline in a 242 gallon tank
carrying 17 gallons diesel 17 gallon tank
full water tank - 40 gallons
2 adults & 1 yellow lab


Post a reply

At idle I go about 6 knots on both engines , with one I go about 5 knots , so I can burn half the fuel just by losing a knot . With only a slight increase of rpm I easily get 7+ knots on one engine . With only one engine in gear the stern will squat down as much and seems to glide though the water easier . The fact I put off much less wake seems to verify this . That may canncel out the added drag of the rudder at angle .

RWS, I didn't see your attachment on your post.

I don't have an exact LWL for the boat, but assumed it to be in the 35 to 36 range, since my LOA is about 39. Based on that, I calculated a max hull speed to be between 8 and 9 mph. At approximately 1500 to 1600 RPM's with both motors, I cruise at about 7.8 to 8.2 mph. I do not have a flow meter, so I do not know what my current burn rate is at that RPM. With one motor, at again 1500, I slow to about 6 mph. Both my carbs need to be rebuilt, so I will probably put the flow meters on then.

If I do run one motor, I can adjust my packings to drip more, and I am not concerned about the Velvet drive Free-wheeling. Its the Walter V-drive that I am more concerned about. If I could run 8 mph (1550 RPMs) and burn 7 to 9 gph I'd be happy. Gas prices in this area are about $4.95/gallon.

At this rate, a 40 mile trip will take 5 hours, and you would burn 35 to 45 gallons of fuel. At $4.95/gallon, you're looking at $173 to $223.

At 3100 to 3300 RPMs, I'm running about 20 MPH, and probably burning 32 to 38 gph (I'm taking this off a previous post of someone running a flow meter on a 10 Meter Mid-Cabin, which is probably lighter than my boat). I'm down to 2 hours of travel. Now you're burning 64 to 76 gallons of fuel over that 2 hours. At $4.95 gallon, I'm looking at spending $316 to $376. That's about $143 to $153 MORE in fuel.

If this is all accurate (which I need to buy a flow meter) that is certainly some significant savings.

Now lets see, a diesel boat would burn about 2 to 3 gallons per hour and only costs $4.25/gallon. Although at about $100,000, that may take awhile to make back in fuel savings.

There is a 136 footer in our fleet and the captain lost one of the mains. She had to motor back on one engine but after about 2 hours she burned up the dripless shaft seal on the dead engine. There was a crossover valve that she forgot to open that cools the seal. The boat had to be hauled, shaft backed out, and the bearing replaced. That was about a 10K mistake.

I believe drip less packing and dripless seals work quite differently. Dripless packing tends to not overheat.....