Twin 40's On a C-22

[hammerhead]

Well took the Hammerhead out on Lake Tahoe yesterday and what a beautiful day it was. Im just wondering if I can get some feedback on twin 40 honda power. What RPM do you cruise at? and what is your cruising and top speed at what rpm?

Thanks

[Captains Cat]

I've got a '94 CD 22 with twin Honda 45's on it. They went from making 35s and 45s to making 40s and 50s in about 1996. I usually cruise at about 4300-4500 RPM, gives me about 16 knots. WOT is about 5800 and gives me close to 30 knots depending on sea state/wind, etc... The speed/ RPM curve gets real vertical near the top end...

Charlie (those are knots, not MPH)

[SEA3PO]

Lake Tahoe like Lake Almanor (where I live) is not the place to worry about rpm and top speed.... you won't get it.... altitude... I am not sure what Tahoe is but Lake Almanor is at 4800' and my 22 with twin 40 Yamaha's suffer some from altitude....what the heck...it still goes and I am kinda a low stress sort...
so I hardly ever worry about stuff like that..

Joel
SEA3PO

[CAVU]

Hammerhead,
My results are almost identical to Charlie's. At sea level in smooth water, I cruise at 4200, 15 kts. My top end is 5800 but only 26 knots.

[Sea Wolf]

Hammerhead-

Lake Tahoe is at an elevation of 6200 ft.

If I remember correct, the rule is an outboard loses 3% of it's horsepower for every 1000 ft increase in elevation due to having less oxygen in the air. (Larry H can confirm this.)

You would lose 18.6% iof your 80 horses at that elevation, about 15 hp.

This should be noticeable in both your WOT rpm and speed, and if you're familiar with your boat, you won't need a bunch of dials, gauges, and digital read-outs to feel the difference.

For those who want to operate mostly at higher elevations, the carburetors can be re-jetted for a leaner fuel mixture, which will help the engine run smoother and more efficiently. It willl also idle much better. Props can be changed, too, to accomodate the hp loss.

The lean jets must be replaced with the normal ones when returning to sea level type altitudes, however, or the engine will run too lean and therefore too hot and burn the pistons and cause other problems. The props must be changed back as well.

Note: fuel injected engines automatically compensate for elevation changes and obviously don't require re-jetting, but suffer the same hp losses.

HTH Joe.

[hammerhead]

Thanks, thats good to know, I cant even tie knots let alone drive um

[Larry H]

Joe,

As I recall the HP loss is 3% per 1,000ft. above 1,000ft. That would make Lake Amadore about a 15-16% loss. Atmospheric pressure and temperature also has an effect. Cold, high pressure air has the most O2.

If I were to operate a lot at a high altitude lake, I would prop for sea level and also have a second set of props(lower pitch) for the lake.

[Hunkydory]

Run Honda twin 40's. Routinely go from sea level to Yellowstone Lake which is approximately 8000 ft. Most of the other lakes we frequent are are between 2200 and 7000 ft. Started out with the different prop thing for different elevations and weight loads. Had 3 different size props still couldn't match up for all situations. Switched to the adjustable pro pulse props. Couldn't be more pleased with them. Can quickly fine tune them for any weight or elevation we've run. On Yellowstone Lake with 5 adults and gear adjusted to 5400 rpm max throttle, which equaled 18 mph. Can comfortably cruise between 12 and 15 mph. Can't remember the exact rpm, but its in the 4000 to 4500 range.

Would prefer more power when extremely loaded at sea level or at 8000 ft. If we were to repower it will be in the 100 hp combined range.

[hammerhead]

Yes I found the C-Dory website gives all the specs for rpm power ect, was not aware of the elevation factor. You guys are priceless. I have been told at sea level with twin 40's you get 31 mph at full speed around 6000 rpm and cruising at about 22 or 23 at 4500 rpm. Thats plenty fast and I cant wait to get out salmon fishing next weekend.

thanx again all

[Dora~Jean]

[jimandlaurie]

Jay And Jolee on Hunky Dory ,no real comment on the 40's ,but since I see you are in my Native State, have you had your 22 on Pathfinder or Alcova Lakes? These were the lakes I grew up on as a boater with my folks. We spent most of our time on Pathfinder..so much that both my parents are now a part of Pathfinder per their wishes.

[Hunkydory]

Capt. Jim & Adm. Laurie

Sorry to say, we haven't been there yet. Plan to in the future. We live in the far western part of the State and with working 6 days a week, it will have to wait. Any advice about either lake would be appreciated.

[Tony]

I have twin 40 on my 2002 22, calm water W.F.O. 5100 rpm 30 mph. 22 mph at 4200 rpm gets the next best fuel economy to the 17 mph 3??? rpm cruise. But I have no trim tabs, yet.
What about weight in the bow? I have 250 lbs #8 shot. Thought about adding 100 more. This changed the handling of the boat so much in 3'-6' C.G. waves. The first summer with my boat I tried to cross a channel into the lea of some islands. I was quartering into the wind C.G. 4' The first two or three waves that came over the bow and smashed off the wind shield got your attention but the next wave just picked up the bow and tawsed it down wind slamming my head off the side window. I went home with my tale between my legs... Our dealer recommended the shot and I thank him for that. The boat is so much more stable and we don't flinch at C.G. 4' anymore.

[Sea Wolf]

Tony-

250# of 8 shot, eh? Ought to hold down the bow a bit!

I've got 74 lbs of chain, 10 lbs of 1/2" line, a 10 lb anchor, a 5 lb bow roller, and sometimes up to a 150 lb dog up there and can empathize with your solution to the wave / chop problem.

Eliminates a lot of the need to use the motor-hydrofoil and/or trim tabs adjustments to cut the waves!

One question: can't quite figure out the term C.G. Waves (?)

Coast Guard ? Computer Generated ? Center of Gravity ? Capillary Gravity (real term!) ? Call Girl ? Cape G________ ? CXXX GXXX (four-letter word? I understand WFO!)

The doiwnside to adding big time weight up front for this purpose is that with the waves astern or at the rear quarter, the bow tends to dig in as the waves lift the stern, causing the boat to roll and broach.

This is not a problem on a small lake or limited sized bay, of course, but you'll find there's a great deal of agreement this is a definite no-no on big water and waves if you read through the various topics discussed within the "Trim Tabs and Hydrofoil" and "Helmsmanship" headings in the Library section of the Forums.

Your future trim tabs are a better solution than adding more weight, but have their own drawbacks off the wind too, as they accentuate the lifting of the stern, unless they can be completely retracted. Lots of discussion of this in the topics mentioned above!

Joe.

[oldgrowth]

I don't feel so dumb if Joe doesn't know what CG is. I thought everybody knew what it meant. Was too embarrassed to ask and I figured I would eventually learn what CG is. Now it may be sooner than later.