Motor hour use time on twins vs single while slow cruising

[Hunkydory]

This year in our combined boating travels in SE Alaska, the Yukon River & Lakes Yellowstone & Powell, we put 2347 miles on the water & towed it for 6613 miles & while doing so, spent 96 nights sleeping aboard & 193 engine running hours on each Honda 40 motor. In another thread the subject of yearly hours on the motors came up & that got me to thinking, if we had a single instead of our twin Honda 40's, what would have been the hours put on it vs our twins. So with a known accurate percentage this year of 14% at planing speed on both engines & 86% running on one at displacement speed & the total combined engine running hours being 386, I calculated it to be 359 hours if we had been running a single motor of near equal hp to our twins combined.

With now having 2115 hours on both motors & over the years of their use, the best estimate of their use percentage, between one vs two running, being 70/30 %, coverts the twin engine usage to a single of 2115 hours to 3595 hours. It's interesting to see, if we would have chose a boat back in 2003 with a single instead of twins, we could be nearing a second repower, instead of a first.

Of course this only holds true, if one chooses to run a high percentage of their run time, like us on one motor at displacement speed.

Jay

 

[hardee]

Jay, That is really interesting. You keep such good records. I didn't realize that you spend so much time running a single OB. When running single, do you raise the other one? You have more nights on board, this summer but interestingly, our engine hours are very close to the same. I had 188, with approximately 25% of the time on single. Since changing to a higher pitched prop (11 5/8 X 11), I have run more single time and it works for traveling slower and quieter. Running both at idle is not as smooth as a single just up off idle IMHO.

Harvey
SleepyC :moon

 

[Hunkydory]

Harvey

When running one motor, I have found steering to be much better & also easier on the auto pilot, if both are down with only a 1 to 2 tenths of a mph reduction in speed from the increased friction of the non running motor being down too. When exploring in shallow water or other situations where the increased risk to the props outweigh the better control, I raise the motor not running. During the first few years, I always ran with the non running motor up, due to thinking, I was putting unnecessary wear on it's lower unit, but upon talking to a Honda mechanic, who assured me that wasn't the case, especially if the non running motor was in neutral, I switched to both down most of the time.

Also because we run so much at displacement speed on one motor, I prefer to keep the rpm between 3000 & 3200, which with 10"x12 pitch props, makes for 7 mph or slightly over. Lower rpm would make for more quite cruising, but I'm of the opinion the motor needs to work hard enough to keep temps up, preventing gas build up in the oil. I would like to hear reasoning that would change my opinion on this as slightly slower & quieter would be preferred by us both.

We enjoy the slow cruising, but the main reason we first starting doing it was to extend our cruising range, so we could stay out from marinas for longer time periods exploring the more remote places. With carrying extra fuel we have cruised between fuel stops for 405 miles & still had a good reserve left, when finally stopping to fuel. Pretty good for a CD22, that many consider 160 miles to be the max.

Jay

 

[Foggy]

With twins, it is not recommended to leave a non running engine
lower unit in the water because of ''reverse flow".

From Honda manual:

"MULTIPLE OUTBOARD MOTORS

On boats equipped with more than one outboard motor,
all motors normally operate at the same time.

If one or more motor(s) is stopped while the other(s) is running,
put the stopped motor in “N” (neutral) and tilt it up so its propeller
is above the water's surface.

If the propeller of the stopped motor is left in the water, it may turn
as the boat moves through the water, causing a reverse flow of water
from the exhaust side. This reverse flow will happen if the stopped
engine's propeller is in the water, its gearshift is in “R” (reverse), and
the boat is moving forward.

Reverse flow can cause an engine malfunction."

Aye.

 

[PaulNBriannaLynn]

We had the bay star system steering our twin Honda 40s, and with one engine trimmed out of the water it waymore difficult to turn. I usually left both engines in the water with the non running one in neutral of course, making it easy to turn one off and fire up the other to alternate motor use. Never had an issue in 4 years and hundreds of hours of operating it that way.

Salmon fishing was our thing when we weren't doing other activities like camping or shrimping, but I would estimate that 75% of the hours we spent running our boat was trolling for salmon. We always used one engine for that, so our accumulated hours would have been a lot higher had we been trolling with a single that whole time.

 

[Sunbeam]

That's really interesting. I like how you've kept all the numbers, and now - while you're not out boating - you can reflect upon them (and include us )

Just to put in another thought: Into the "we could be looking at our second re-power instead of our first" maybe something could be added for the (estimated) 25% higher cost of powering/re-powering with twins over a single. I know that's not exact, and there are kickers to consider. But when I bought my boat I *really* wanted twins. But the boats I found with twins were unsuitable, and the ones that were checking off all my wants didn't have twins. So when I bought mine (with single/kicker) it was with the idea that "I can re-power whenever I want and even go to twins if I want" (I promised that to myself because I bought a less expensive boat that didn't have the exact engine setup I thought I wanted, but was exactly what I wanted in the other ways).

When I looked into re-powering, twins cost maybe around 25% more than a single (re-using existing kicker with single). That would not stop me if I really wanted them, because the boat is for pleasure, not logic; but as it turns out I found the swim platform to be so valuable to me that I decided to stick with a single/kicker. I don't remember exact numbers (and they would be variable anyway) but it was roughly a ratio of something like $9,000 to $12,000.

Just wanted to throw that in though, to perhaps be included in the theoretical figures.

I still think twins are nifty!

PS: To throw another variable into the mix, what if one had a single/kicker setup, with a deluxe kicker (controls, electric start, etc.) and then when running slowly used the kicker. Then you could re-power the big engine even less frequently, if desired.

 

[MikeR]

It's interesting to see, if we would have chose a boat back in 2003 with a single instead of twins, we could be nearing a second repower, instead of a first.

Of course this only holds true, if one chooses to run a high percentage of their run time, like us on one motor at displacement speed.

Jay

Cool numbers! An analogy would be if you had bought two identical pairs of shoes at the same time and alternate wearing them each day. The two pairs will last twice as long (time-wise) as if you had bought just one pair and wore them every day. You still bought two pair of shoes, but got the second one at 2003 prices instead of 2016 prices. (and having bought a new 50 hp in 2014 and a new 90 hp in 2016, there's not a lot of price difference in the two power ranges these days, a 40/50hp is definitely not half the cost of a 90!).

-Mike

 

[potter water]

When running Still Crazy at any speed, I always ran both motors unless I was in an area where stone whales and rocks may have been. I don't see an advantage or disadvantage on keeping one off. I try to wear twins out as a pair because I'd repower with a new pair. Although now I'm driving a ranger 21 tug with a single diesel. I don't think engine hours are hard on and engine, rather, load. In the case of only having one down pushing at hull speed, that engine is being more heavily loaded than with two down working half as hard. I have no statistics nor evidence, just what to me makes sense.
Engines that are half loaded all the time will last longer?

 

[rogerbum]

With twins, it is not recommended to leave a non running engine
lower unit in the water because of ''reverse flow".

From Honda manual:

"MULTIPLE OUTBOARD MOTORS

On boats equipped with more than one outboard motor,
all motors normally operate at the same time.

If one or more motor(s) is stopped while the other(s) is running,
put the stopped motor in “N” (neutral) and tilt it up so its propeller
is above the water's surface.

If the propeller of the stopped motor is left in the water, it may turn
as the boat moves through the water, causing a reverse flow of water
from the exhaust side. This reverse flow will happen if the stopped
engine's propeller is in the water, its gearshift is in “R” (reverse), and
the boat is moving forward.

Reverse flow can cause an engine malfunction."

Aye.

Note this is only a problem with the gear shift in reverse. Who would leave the second engine down and off with the gear shift in reverse? I always shut down in neutral. When trolling, I nearly always leave the second engine down to slow the speed.

 

[Aurelia]

So I am hearing you would have 70% less hours on your twins if you had a kicker you could run on for the slow cruising (which many single owners do) but would likely want some charging ability on that motor as well.

I think the extra cost of replacing twins balances out any savings due to delayed replacement but it is an interesting contrast in ownership.

Greg

 

[Hunkydory]

Foggy, "what Roger said" though at displacement speed, even if accidentally some how it was put in reverse, I doubt the force of the water would turn over the motor enough to create water flow into the engine. Now a friend of mine has twin Yamaha 250's on a 26 foot Hewescraft & it is unsteerable with one motor raised. It really moves along on the one 250, so if the off down motor was in reverse, no doubt it wouldn't turn out good, but as he's a retired mechanic, he's even less inclined then perhaps the rest of us to put the motor that is off in reverse. That said, it's always good to see just what the manufacturer recommends, so thanks for the post.

Paul, I find it interesting that you have difficulty steering with one motor up with the Baystar steering unit, as that's the unit I have too & for me the ease of moving the wheel is about the same no matter the position of the motors, though I've heard from others like the one, I referenced to Foggy, that have similar or worse than you.

Sunbeam, yes lots of +'s & -'s in twins vs single usage, so it comes down to personal preference of which, several items tip the scale in favor of twins for us, but I prefer the twins mostly because, that's what I'm use to now after 14 seasons of running them & like you, like the "look".

In my opinion, the downside of your deluxe kicker idea is no matter how deluxe, it isn't going to steer the boat as well as the larger twins with both down & one running. They are good for trolling & for emergency back to safe waters, but not for long distance & time slow cruising in areas such as SE Alaska on a boat like a CD 22. Now I imagine a small kicker type motor on a matching sailboat just the ticket. Though the better the set up, the more favorably it will compare on a CD22.

Potter Water, my statistics & evidence is lacking too on a debate, between whether running at displacement speed with twins on one motor running or both is the best choice, but the preponderance of the discussions, I've read & heard on this & my own opinion is running one motor at a time with twins at displacement speed is the better of the choices. I wish at least on fuel usage, that someone could provide good records running both ways over a substantial time period. I know when we're in rougher sea conditions any advantage thought to be gained by running on one motor for overall cost savings is not worth it, compared to the added control gained by running both motors. One motor running is done only in what we judge to be applicable sea conditions, which in the last two seasons has been near 87% of our total running time. I agree that engine load has much to do with engine longevity & fuel consumption, but we differ in the preferred amount of load. My choice is to run one motor at a time at the higher load, so as to work it just hard enough, that switching between the motors often or needing to run them several times during the day at a high rpm is not necessary. In doing this, I tend to run one motor for the majority of the day if not the whole day, using time over the long run to balance out the hours. This also prevents the many cold starts one has to do if making frequent switches. I will continue to do this my way, until I receive good data to change. Until then the advancing trouble free engine hours will have to be my conformation of at least if not the best method, at least not harmful either. So far, at 2115 hours & their never having ran smoother, l'll maintain this course.

All the service maintenance & most other maintenance has been done by me on our CD22 & I plan on running these motors until a major repair is needed. I'm hoping that doesn't occur until at least the 3000 hour mark or higher. So far the 1999 Honda's have been amazedly trouble free with most of the work done on them being preventative maintenance. By doing my own work, I've already saved in service maintenance alone, near the cost of one replacement motor.

Greg, if this is what you are getting from this thread, I suggest you reread my reports of our travels & see if you really think any standard kicker set up would have safely maneuvered us or anyone else 70% of the time to all the places we've been at a boat controlling speed of 6 to 7 mph & yes the battery charging is a necessity too. Of course a large single would have at displacement speed, but no way with a standard kicker.

Jay

 

[thataway]

The rotating the lazy prop, with gear in reverse to turn over the engine would only happen with boat at planing speed--not with the slower speeds that Jay has used. There are some boats with twin 350's where this could be a reality, but to crank one of the Honda 40/50 in reverse, is beyond the hydro dynamics of this situation.

I had thousands of hours of sailing, with a prop which could have rotated (but would have not turned the engine, because of the type of transmission.) These were 24" three blade props, with many times the surface area of the prop on an 40/50 hp Honda. Even turning an alternator with the large prop (lets say getting 5 to 10 hp) is difficult but can be done, at higher speeds. We always locked the prop shaft because of vibration and potential damage to the transmission output bearings, rather than any other reasons. In our case the lubrication of the transmission was from the input shaft, and there would be damage if the blades were allowed to free wheel at higher speed for any length of time to allow heating of the transmission oil/bearings.

Free wheeling a small outboard prop at low speeds will not cause any damage to the lower unit or gears. In June 2015 a study was done to find out the drag of a free wheeling outboard prop vs fixed prop. This showed conclusively that:

wherever possible you should let your fixed three-blade prop spin. The drag when it was locked was nearly three times the drag when spinning, and the loss of speed was over half a knot at 4 knots, and extrapolated to be 0.75 knot at 6 knots.

Certainly interesting observations, and for Jay's type of cruising it makes a lot of sense for the twins. It would have been interesting to have another 22 along on exactly the same voyage with the single outboard, to see what fuel consumption would have been...When crossing oceans a number of limited range trawlers have run engines alternately. A Grand Banks going from Hawaii to Seattle, actually took the prop off the one engine--and then in mid ocean, shut the driving engine down, took the prop off, continued the voyage on the other engine, after its prop was placed back on the shaft.

 

[Sunbeam]

Good point on how the "deluxe" kicker wouldn't work well for what you do. So then it's back to (for the sake of this discussion) the idea of a single main (with perhaps a kicker for backup) and then how would that pencil out over a longer period of time as opposed to the "use one then the other" way with the twins.

I didn't figure this was the typical "single vs. twins" discussion (heaven knows there are enough of those already), but rather a specific angle on it, which is "which costs more in terms of gross re-powering costs when you tend to run slowly: Alternating twins, presumably re-powered less often, or a single used every day and thus re-powered more often?" I was just bringing up that it costs less to re-power with say, a single 90 vs. a pair of 40's or 50's. Just because I didn't see it mentioned in the first post.

Always interesting hearing how you do things -- and one certainly can't argue with over 2,000 hours and still purring like (twin) kittens :thup

 

[Aurelia]

I did see the speed you travel at Jay and it does sound faster than the standard kicker put-putt but... you also seemed open to running slower if there were no ill affects on the engine so that "might" equate to the use of a lets say a popular 10hp kicker which would push your boat without making too much noise.

I know you venture to remote places, but that's what the oars are for!

That 7 knot speed in our boat is a slightly noisy one and just a little more than slow for the 19. We find the hull to prefer about 4.5-5 knots and taking significantly more power to get over that.

Greg

 

[Hunkydory]

So then it's back to (for the sake of this discussion) the idea of a single main (with perhaps a kicker for backup) and then how would that pencil out over a longer period of time as opposed to the "use one then the other" way with the twins. :thup

For us the twins work to our advantage over the single with a kicker, but very few others would approach the 86% average slow cruise use we have done on the last 5 long extended SE Alaska Cruises, so for most, I would say it's a mute point, but for discussion sake, if use rate & hours were similar to our last 5 Alaska cruises the advantage would be toward the use of twins, though as the slow speed rate of use drops, it would rapidly go to advantage single. Overall, I'll readily agree, for most the good looks of the twins come with a higher price, beyond the original cost.

Jay

 

[Hunkydory]

Greg, I appreciate this additional post, which enables me to see & understand the point you were making. I did say that I would like to hear reasoning about alternatives that might make slower & quieter possible & I apologize for reacting poorly to you suggesting another way.

I also agree that 4.5 to 5 knots is a very pleasant speed, but the distances that need to be covered on a average daily run in SE Alaska require more often a slightly higher speed & much of the time, there's no choice, but to make headway into a tide, that requires 6 knots to even make 3 or 4. Also, often the sea conditions would be ok for easy running & steering with twins with both motors down & one running or a big single, but very poor for a 10 horse kicker mounted off center. As smooth water conditions deteriorate, we go from both down one running to both running, then either way down on speed or up to a partial plane or plane for best boat control & comfort. I have not seen anyone else attempt to cruise for lengthily periods in SE Alaska on a kicker, other than when trolling for fish in a C-Dory type boat, but if any have, I would be interested in their report of doing so. Then again it's just plain rare to see a CD22 size boat anywhere there, that is not in a fast running distance to the nearest town & Marina. Other than a tiny fraction, the other cruising boats we have met are in the 35 foot plus range. Even if a more quiet adequate speed could be maintained along with battery charge, I really doubt the steering with a off center 10 hp motor would be workable over a cruise of any extended distance.

Jay

 

[Sunbeam]

I'm enjoying the discussion and the additional thoughts and points. Very interesting. As you say, so few people are cruising as you do in "tiny" boats (as compared to most) that some of the engine use characteristics are rather unique, and not discussed as much elsewhere.

Overall, I'll readily agree, for most the good looks of the twins come with a higher price, beyond the original cost.

But they do look so darned good*. I was somewhat crushed to discover how much I used the swim platform (that's to port of my main) and how handy it is --- because I was pretty much set on re-powering with twins. Well, I haven't re-powered yet, so who knows

*And of course for your cruising, as you've explained, it's not all about looks - didn't want to imply that.

 

[DrewbirdII]

Jay, I know I'm no expert on motor wear and tear, but aren't your motors propped for both to be running to meet your optimum rpm at WOT. I would believe running only one engine would be hard on it, like driving up hill in high gear? A larger motor would hardly be working at 6 or 7 mph. If 70% of your boating is done at that speed it should last forever! Just a thought.

Jim.

 

[Hunkydory]

Jim, I'm not an expert on motor wear either, but I know enough to say you would be absolutely correct, if I had chose to try & run just the one motor at speeds much above displacement for an extended period of time, but with 12"x10 pitch props at 3000 rpm & 7 mph, not knots per hour, it is just running with enough load to maintain good function. If facing a short stretch where more speed is needed, I will boost the speed for those conditions for a very short period, but if I continued to do so lugging damage could result. In an emergency, such as loosing one motor & having to get to a safe place in bad weather & rough seas, I would push the motor as much as needed to maintain steerage & boat position on the waves & be darned glad, I was doing it with an over pitched prop on a 40 hp motor than a kicker with 6 to 10hp.

We have now cruised in our CD22 for 18,100 miles & at least 12,000 miles of that has been at displacement speed on one motor only running. I suggest, if what you think is accurate these motors with 2115 hours on them would have long ago had to be replaced instead of seeming to purr along, like the 1st day we ran the boat in 2003.

Jay