twins on a cd 25

bcarli · Posted: Mon Jun 19, 2006 10:29 pm Post subject: twins on a cd 25

Hi
Is anybody out there using twin engines on their cd 25? I do a whale watch business with my 25 and with 6 big people on board the 135 doesn't make it.
I doubt this is a prop problem, I think I'm just to under powered to get up to cruising speed. I'm running about 15 knots at 5300 rpm. Ouch! fuel economy
is terrible.

doc · Posted: Mon Jun 19, 2006 11:02 pm Post subject:

Hi. How clean is the hull. We have had 6 on our 25 with a 140 Suzuki and it will do pretty well, that is, unless the bottom is furry. Then, its 14 knots with even one on board. I agree though, that it would be nice to have some extra power.

Valkyrie · Posted: Mon Jun 19, 2006 11:24 pm Post subject:

Sea Angel was at the East Coast Gathering and had twin 90's (Hondas) on his 25.

Maybe he will see this or you can send him a PM.

Nick
"Valkyrie"

JamesTXSD · Posted: Mon Jun 19, 2006 11:41 pm Post subject:

Interesting discussion. The factory folks recommended the 135 for us. I did tell them that top end wasn't our priority, but 15 - 20 knot cruise is important. Is that a problem with the 135? (We will rarely have more than the two of us and cruising gear onboard.)

Best wishes,
Jim B.

Dora~Jean · Posted: Mon Jun 19, 2006 11:49 pm Post subject:

Hi Bill,

I have twin Yamaha 4-stroke 80's on mine. The boat is powered just right, plenty of power. On average I like about 16-18 knots, about 4200 rpm I think. I have carried up to 6 people, 2 of which were children, overnight gear and all. I have tried raising one engine and running on just one 80, at about 5,500 rpm I can get about 15-17 knots, but that was with only 3 people on board.

I like twins for open ocean travelling which is 90%+ of what I do. Islands are 20-50 miles off shore.

Ron on Meander · Posted: Tue Jun 20, 2006 1:11 am Post subject:

With almost 1200lb of people (4 xxx and 1 large), full fuel, water, and food for a three day trip our 150 Yamaha easily planes our 25 and can still push the boat up to 28kts top and easily cruise at 20+ at 4500 rpm.
Ron

Stanley-J · Posted: Tue Jun 20, 2006 7:07 am Post subject:

I have twin Honda 75's and with 3 people on board I have show 31mph on the GPS....thats also with a Honda EU-3000 that weighs about 160lbs.

Byrdman · Posted: Tue Jun 20, 2006 10:16 am Post subject:

Bill and Chris: Now just for kicks and grins.... you may want to take a look at the prop.....if you do have a clean bottom on your boat. By clean... I include a boat with good bottom paint that "is cleaned" each time you mover her about at planing speeds.... But... if ya have stuff growning on her.... that is a lot of flat bottom aft that is a big ol drag.

I do not have, or never have owned a CD25, but have traveled on one for a weekend trip....and that was Pat and Patty Anderson...and I know they have tried several props..

Now, looking at the other single engine CD25s... particuarly the "similary loaded" CD25 with a 150 yama.... (only 15 hp difference)..... there should not be that much rpm/speed ratio differance.

I know there are several threads on props with the CD 25.... but have not really taken the time to read them. A little prop change can mean a whole lot...particuarly if you .....like others have mentioned... have a "general operating" speed/weight load.

bcarli · Posted: Tue Jun 20, 2006 10:42 am Post subject:

Thanks for getting back to me. My wife and I have been life long sailors so all of this pretty confusing at times. The best fuel economy I get is running at 18 to 20 knots, according to my fancy high tech honda gauge. If I'm cruising 18 to 20 my miles per gallon is about 2.4 to 2.6, regardless of how many people on board. Yesterdays trip with 6 large people on board I just didn't have the power to get up to cruising speed. I would love to just re-prop and have this problem go away. I have a 3/14 1/2x 15 prop. Max rpm's totally wide open is 5400.
Also I need to increase my mpg if possible. I often run 40 miles a day on a trip and some days I do two trips. I wonder if with twin engines I could get better fuel economy? I would be burning fuel for both engines but I wouldn't be running at a high rpm and I could get to my best cruising speed in less time, which is when I really burn fuel.
p.s I just did the bottom 3 weeks ago so that's not the problem

Byrdman · Posted: Tue Jun 20, 2006 10:59 am Post subject:

Bill and Chris: Here is another thread with proping out on a CD25... There are several more... Just hit the Forums button up at the top left hand corner of our site....and scrol down a bit.... keep scrolling.... and a whole section...with many prop topics... and not all agree... Go figure.

Another thought is the total cost of changing motor(s)... after sales tax, rigging...and insurance... and maintenance on two "full size motors" compaired to one motor.... IF... you were able to pick up 1 mile per gallon... how many gallons would you have to go thru to just break even? Or.. Mr. Green

you just might want a nice set of twins setting back there... they do look good... Embarrased

You have to also keep in mind you are traveling with a HEAVY load...and not just 2 folks out in their boat for a day trip... Most good prop shops will work with you to a point on trying out a few. If you do not want to try all this with customers on board... you could more than likely get some other C-Dory owners to just go riding with you one day...and you can bring two or three props... and pick the one you like best...and return the others. ...or.... just put some water barrels on board.... they will more than likely have way fewer opinions.... Mr. Green

... but not be near the fun.

Good luck.

Byrdman

http://www.c-brats.com/viewtopic.php?t=2215&postdays=0&postorder=asc&start=0

Dora~Jean · Posted: Tue Jun 20, 2006 11:06 pm Post subject:

Bill and Chris, don't know if the factory is putting larger trim tabs on the 25's or not, but I upgraded mine within a week of my first sea trials to about 50% larger (now 14" wide x 11" deep). Now I can plane down to 8 nmph and adjust for maximum speed vs rpm very easily no matter what the load. My tiny original tabs were pretty much useless under 13-14 knots. THAT alone had a large effect on my gas mileage.