Economy, twin emgines vs. single engine

Gene Stebbs.

t has been over 35 years since I have had REAL boat under me, I ran a 34' refitted steel hull lifeboat with a 300CI ford engine, from Seattle to SE Alaska and back for 5 seasons, 7 knots wide open with the tide and wind on your back side, with no lift at all on the bow with this style, it would however take Noahs flood on the backside and ride in comfort. I hope to pick up a used 24-25 ft. C Dory, hopefully within 3 years or so as family health conditions allow me the freedom to do so. My knowledge about the larger outboards is nill, and my main concern is economy as I may end up running the boat back and forth from Washington to SE AK. I would like to know what the most economic size engine for a 25' C Dory would be, keeping in mind that cruising a 12mph is fine with me and on flat water I do not need to run at 30-40 mph. Also what loss in economy is there when going from a 150 HP single engine to a pair of 75's. Thanks in advance folks, it sure seems to be nice group here and quite knowledgeable as well. I will be around picking your brains from time to time, hope I do not wear your collective patience out to soon. A good day and happy boating to all,Gene.

BrentB · Posted: Wed Jul 29, 2015 5:22 pm Post subject:

Gene

Just wait and you will receive a wealth of info. In the meantime read the archives

ghone · Posted: Wed Jul 29, 2015 5:46 pm Post subject:

Welcome, you've touched on one of the most asked questions, lots of info in the forums
The 12 mph is likely the worst speed for a cd25, hopefully 25 owners will chime in
Great mileage is available at hull speeds of around 6 knots and the 25 seems to get 2-21/2 mpg from most owners when planing at 12-14 Knots
Top speeds loaded will be way less than 30 mph, we see 25's with anywhere from 135-175 hp, likely better performing all around with 175 available, the 25 is pretty heavy I think I've seen more singles on 25's than twins
Welcome to your quest, I'm a single engine guy with a 22 we see anywhere from 6-7 mpg at hull speed to 3 1/4 -3 1/2 mpg at 15+ knots
George

Avidmagnum12 · Posted: Wed Jul 29, 2015 6:47 pm Post subject:

I have a 200 hp Yamaha 2 stroke 2010 HPDI with a 17 pitch prop with Permatrim on my 2011 CD25. It gets about 6 MPG at hull speed and about between 2 and 2.5 on plane. With full fuel tanks and water loaded for a 10 day trip to Isle Royal in Lake Superior the C-Otter was capable of well over 30mph. Yes ...it will go faster. Had it over 40 mph on a WOT test. Not fun! My hull really likes 20 to 25 knots. Followed my friend Hanks nice 22 CD at 15 to 18knots for a bit but did not feel efficient. The fuel burn on a 25 is higher than the 22 I recently sold but my wife likes it better so no complaints

So far the Yamaha has been a great engine. I tow my CD with a 2012 F-150 on a aluminum trailer and need to keep the weight down to stay within towing limits. So twins are not not an option because of weight.

journey on · Posted: Wed Jul 29, 2015 7:09 pm Post subject:

Well, here's a few graphs of C-Dory 25 performance. Just plotted the posted numbers, no massaging or anything fancy. Note that the 25 is sensitive to loading. As we load Journey On for a trip, the mileage goes down.

First, reported mileage at various speeds. Please note that GPM is actually MPG. Dyslexia, I suppose.

Next, Speed vs RPM

And Mileage vs RPM. As you can see there's a little dip when the boat starts to go on plane, from the above graph that RPM is ~12 mph. That dip is not shown above, but I think it's really there.

Boris

JamesTXSD · Posted: Wed Jul 29, 2015 7:16 pm Post subject:

George is right on with that 12 mph speed being around the least fuel efficient. We had a fuel flow meter on our 25 (Honda 135), making it possible to trim for most efficient fuel burn at a given speed.

Most of the time, we were loaded for cruising - these boats do feel the extra weight. Best over mpg was at displacement speed, around 6 knots, getting around 5 kmpg. 1800 to 2000 rpm was efficient, 2200 rpm wasn't... a small bump in speed and rpm makes a real difference in fuel burn. On plane, we found 16 knots (wind and wave conditions will also make a difference) gave us a fuel burn of 2.5+ kmpg.

I don't think there is much, if any, penalty for twins vs a big single regarding fuel economy, if trimmed for best mpg. I liked the idea of twins when we ordered our boat (at the time) in 2006, but the Honda 90 hp motors then did not have EFI. The factory folks asked how we would be using our boat and recommended the 135 hp (not looking to do constant fast cruising). The only time I wished for more power was at high elevation lakes, like Yellowstone or Lake Tahoe.

When we first got the boat, lightly loaded it would exceed 25 knots with no problem, but that speed felt a little uncomfortable to us. Pull back to 20 to 22 knots and it was quieter and more comfortable. 16 to 18, even better.

We sold our boat last year, but if in the market for that size boat again, I would absolutely go for it. The CD-25 hit all the important points for us, regarding: comfort, seaworthy, economy, trailerable, liveability.

Good luck with your search.

thataway · Posted: Wed Jul 29, 2015 8:12 pm Post subject:

The "mileage" with twins and singles are more dependent on the loading of the boat, the trim, the bottom condition, etc, than the twin vs single.

Now you might say, I want to run one of the twins, at 5 to 6 knots and go for best economy. Again, I will say, it depends more on trim, loading etc, than on a 75 vs a 150.

On the Inland passage, where you do want planning speeds (15 to 25 knots)--is when going thru the passes. If you have a boat doing 5 knots, you will probably do one pass at slack water a day (some require high slack water). With the capability to do 22 knots, then you can do 3 major passes a day. That may not be important to you. But it is important on resale, that the boat be able to plane. The early 25 cruise ships (about 5 of them built in the mid 90's) often had a single small motor. The vast majority of these have been repowered with larger engines.

Gene Stebbs. · Posted: Wed Jul 29, 2015 8:17 pm Post subject:

thanks for the quick replies, I will spend a lot of time in the archives as it has been a long time since I have skippered more than an old 18' wooden hull rig fishing on some local lakes the last dozen years or so. I did like the looks of the Sea Sport but could not see any need for the extra weight, hull area, for playing around SE AK, Even with the 25' CD I wonder if the trip up and back from Seattle might not burn more fuel than I would burn during the 3-4 months I plan on fishing, hunting and visiting my daughter in Wrangle, I really like the capacity of sitting the boat on the beach thru a tidal cycle while doin' my "thang" ashore........thanks again for the replies folks, please do not hesitate to call me on a flub if I head toward a dead wrong, boneheaded,game plan....it has been a long time..Good point on going faster than the tides, almost got jammed up running the Yuclata rapids (sp) in "78 or "79. boat did 8 knots tide ran 10-12....all ahead backwards

T.R. Bauer · Posted: Thu Jul 30, 2015 2:01 am Post subject:

Don't get me wrong, I love the CD 25 as it is a lot of boat for the money. But with that said, you might want to look at CD 22s as they are significantly more efficient, easy as it gets to trailer, plenty capable at sea, but they don't have a head or shower- which I could care less about as there are very simple alternatives.

SEA3PO · Posted: Thu Jul 30, 2015 12:10 pm Post subject:

I get 4.5 using twin 40 Yamaha motors....at about 3/4 throttle ....
I would never ever buy an outboard with a carburetor.... fuel injection is the only way to go... I like the twins on my 22 cruiser...makes it easy to handle... and also a margin of safety..... several times we have had one motor or ta other give us a problem and it is nice to have the other to get ya home... (darn carbs)

Joel
SEA3PO

SEA3PO · Posted: Thu Jul 30, 2015 12:15 pm Post subject:

I have never been thrilled with the Yamaha carbs... just before the Delta I got mad at em and decided to fix em or destroy them... so I pulled them apart and did a re-jet.... I really changed the sizes of the jets...I expected the motors to run better and faster...but never expected to get better fuel mileage...it was amazing .... they ran great and appear to have gotten much better fuel mileage....just goes to show you what YAMAHA had to do to get the emissions down... too tight for the motors to run well...they now fly...

Joel
SEA3PO

Gene Stebbs. · Posted: Thu Jul 30, 2015 4:37 pm Post subject:

I have thought about one of the smaller boats, I plan on living on it for 4 months or more out of the year so the xtra room is one of the factors, I have had on my mind, but nothing is etched in stone at this point.Between the archives and all the experience on this forum and my having to "relearn" so much, who knows what my choice may be 3 years +/- down the pike. Again all comments,suggestions are appreciated and will carry much weight toward the end product.

PaulNBriannaLynn · Posted: Thu Jul 30, 2015 5:27 pm Post subject:

The 22 cruiser is about the smallest potential live-aboard out there. There's plenty of folks on this site that have full timed in theirs for long periods.

Even though we're minimalists and even call a tiny beach cabin home, I'd need a bigger boat to live full time in it. We love our 22 for what it is, but after about 9 days I'm feeling claustrophobic, a little crusty and hobo'ish. Everyone is different.

Most of the twins vs. single debate on this site has focused around the 22. For the 25, the majority of them have singles. I have seen a few for sale with twin Honda 90s. There was a discussion here a while back about the 25 with twins and people thought the performance and power to weight on a 25 was better with a big single.

Id do an long term Alaskan trip in a heartbeat but would trade up to a bigger boat first.

ssobol · Posted: Thu Jul 30, 2015 6:52 pm Post subject:

Nothing wrong with being a little "hobo'ish". Shows you that you can get along fine with much less stuff than you might think.

johnf · Posted: Thu Jul 30, 2015 11:33 pm Post subject:

Hi Gene,

If want to see a 23 Venture feel free to give me a call...I'm over here in Tigard. Had a 22 Cruiser for 10 years and just moved into this earlier in the year.

I have it in storage just near the Washington Square Mall. Should be around Saturday morning/afternoon but busy in the evening. Or we can try for some evening during the week.

Wasn't sure if have been on the 22, 23 or 25 yet so glad to help.

Kind Regards,

John
five OH three - seven twenty - four zero nine zero