I'll Bet Anything...

K

k3nlind

New member
... well just about anything... that this has been asked and answered a number of times before... but search brings up over 500 hits and most are not what I want to know... so...

Why does the factory place a 100HP limit on my CD22 :?: I see smaller boats with more and I see weaker built boats with more. :shock: Does anybody out there run more than 100HP on their CD22 :?:

thanx, :wink

ken
 
Ken-

The boat was originally designed for 70 hp with a FLAT bottom.

In 1987, the new Cruiser and Angler came ut with a very shallow 2 degree v-bottom at the stern. At this point, recommended hp was 70 with a max on the label of 90.

A few years later, the max was raised to 100, approx late 1990's.

Today it stands at a max of 115 (raised this last year).

No doubt the hull is strong enough for more, perhaps as much as 150 hp.

But several problems arise:

First, the weight of the larger engine affects resting bouyancy greatly, making the stern heavy.

Second, the boat handles differently in chop, because the added weight changes the dynamic balance. This is contrary to the light in the ends dory design theory which advocates easy climbing over waves.

Thirdly, much more than 90-100 hp with that shallow a hull, and the boat gets squirley, especially due to chine walk, where the motor torque pushes one side of the hull down harder than the other( which it also lifts), and we go skiing on that side of the hull!

Add an inexperienced skipper and your have the recipe for an accident!

Hope this helps answer your question, will get back to this question later, the door bell is ringing!

Joe.
 
I believe that the better question is why would anyone want more than 115 hp on a C Dory? Sea Wolf's explaination is very good. The boats just don't need any more. The C Dory is not a speed boat. I handles well up to 30 mph. The idea is a simple and rugged boat which is seaworthy. I had 90 hp, and it as more than adequate, even with four people 3 dogs and supplies for 10 days aboard.

I agree that if you put too big an engine (weight) or more HP, you will affect the handling qualities. A basic rule is to keep weight out of the ends of any boat--outboards violate this rule just because of the location of the engines. The weight in the ends, decreases the response time of the peroid the hull as it works into seas. In many boats it will lead to hobby horsing, an undesirable characteristic. Granted that you can power a flat bottom boat fast, but the sea keeping ability is compormised.
 
Joe and Bob are spot on IMO. The 22 CD will hobby horse -- and just the thought of a heavy OB and full fuel in the stern and a 28 gal. tank forward gives me hives...

I like the 22 up to about 30K flat out, and my favorite cruise is about 15-17 kts in decent water. It's a great all-around boat - none better that I know of - but a speed boat it ain't.

Of course my AK buddy will totally disagree, and runs 115 hp and loves it -- but my 22 with the 90 E-Tec is a cool package and well-balanced.

Dusty
 
Well, I find all that data interesting and very informative :shock: ... and I like the twin 40's I have on my CD and I have no desire to either ski nor become accident prone, but... many of you are stating that you get 30 knots and cruise at 20. I am getting only 20 knots at full throttle :!: ... a little over 4K RPM. is this what I should expect from twin 40's :?: ... not according to the stats on the CD site. As far as I can tell everything is running quite well, but I am a bit concerned that I might one day wish to join a CD outing... how will I ever be able to keep pace :?: :cry
 
k3nlind-

If yor maximum rpm is at 4k and 20 mph, you're probably "overproped", meaning the props have too much pitch, if everything else is OK. Depending your your motor brand, your maximum rpm should lie somewhere in the 5000-6000 rpm range.

What brand of motors are your twin 40's, and what pitch and diameter are your props? 3 or 4 blade? Is your boat loaded unusually heavy? Is the boat trailered or moored? Is the bottom clean and fair?

Once we know these factors, we can compare your props and performance with other known set-ups and see how you compare.

If you're overproped enough that you're limited to 4k, you're really lugging the engines, which is not good!

Joe.
 
History question here guys.... I know I have this data somewhere...but prepping to close out this house and move forward... so just asking is faster and easier.

My 1985 18' Angler was bought new in 1984 end of season with a 50hp Johnson VRO motor with tilt.

Does anyone know what the weight of that particular motor w/hydraulic tile mechanism weighed in comparison of todays new motor weights?

Same true on the 70 and 90 hp motors.???

Not a show stopper....I was just wondering how weight/HP ratios have changed with technology.
 
Patrick-

Here are the weights from the 1988 Johnson catalogue, in which the weights should be unchanged, as the motors were also:

50 hp vro w pt,pt-20" shaft, electric= 197 lbs

70 hp vro w pt,pt, 20" shaft, electric= 257 lbs

90 hp vro w pt,pt, 20" shaft, electric= 301 lbs

Joe.
 
thanx for your interest and comments Joe...

Somehow I knew that I would need to provide more information. So...

I have two sets of props.

One is aluminum 3x11.1x13. These are currently not on the boat. But as I recall they did let me get close to 5K RPM running full throttle getting about 21-22MPH.

The other set, currently installed, are Comprop 4x10x13. They do about 4500 RPM at full throttle and get me about 22-24MPH according to the water speed indicator. GPS reports only 19-20MPH though. (GPS was not running when I had the aluminum props installed.

The engines are Honda four stroke 40HP.

As for weight, I would guess from reading the site that I may be just a bit heavier than others because my anchor is all chain, about 300 feet. And I have two engine batteries and two house batteries. I usually run with no water. Other than that I would weigh about the same as other 22's.

thanx again,
 
RE: If you're overproped enough that you're limited to 4k, you're really lugging the engines, which is not good!

Sea Wolf - I'm a learner here; could you explain the meaning of "lugging" in the above referenced statement?

In the diesel world "lugging" means running an engine at to low RPM with a load on it.

I don't understand how an engine turning 4000 rpm pushing a load could be considered "lugging", but I would like to.

Thanks,

Law
 
KEN-

That 300 ft of 1/4" G-4 High Test chain at 0.75 lbs/ft = 225 lbs!

Plus the anchor's 10-20 lbs, and right on the bow, and you probably have a windlass, too, with all that chain, right?

250-275 lbs or so in the bow, plus an extra 120 for the two extra batteries....

Well, up front, it sounds like you're a bit heavy to begin with, and especially "up front".



Now lets play with the props:

Start with the 10 inch pitch and figure theoretical speed at 5000 rpm_

10" x 5000 rpm x 1/2.09 gear ratio = 23,923 inches per minute

23,923 inches/12 inches per ft =1993.6 ft/ minute

1993.6 ft/minute divided by 5280 ft/mile = 0.377579 miles/ minute

0.377579 miles/minute x 60 minutes/hr = 22.65 miles/hr

This is for the 10 inch prop at 5000 rpm. You're getting 22-24 on the pitot tube, or 19-20 on the GPS, but at 4500 rpm and we haven't even allowed for the 10-15% slip between the prop speed and the boat speed through the water.

If you assume the pitot tube speedometer is off, and the GPS on, 22.65 mph calculated minus 10% for the prop slippage would give you 20.4 mph, and the 19-20 GPS reading is about right. The only question would be the indicated low 4500 rpm (?)

For the 11 inch prop, we can just take the 22.65 and add 11.1% to it for the change from 10 to 11.1 inches of pitch, which would yield 25.2 mph. You're getting 21-22 mph on the GPS, which would seem right on the money after we take the 25 mph and subtract about 10% for prop slippage.

So what can we conclude?

I'd guess that the 4500 rpm reading was in error, somehow.

I'd also guess the pitot tube speedometer, which measures water pressure in a small nylon tube under water, was overly optomistic, and we would trust the GPS speed more.

If you trust your tachometers, you might try to go down to a 9 inch pitch set of props if your maximum rpms are under 5000, which should raise the max by 550 rpm or so, depending on other variables.

Another thought for experimentation-

dump the 300 ft of chain and anchor (can't easily remove the windlass, if so equipped) and any other heavy stuff, and see how fast she goes w/o all the heavy duty equipment-??? Might just gain 3-5 or more mph w/o new props.

Holding the nose down is definitely good in chop, but takes a lot of extra energy to make the larger waves from the bow plowing deeper through the water.

Hope this helps!

Lots o' fun!

Let us know what you find out.

Joe.
 
Seeker,

I think that what Joe meant is that the props are overloading the motors, or that the props are "lugging down" the motors.

The correct prop for any motor/load will allow the motor to reach its "full throttle range" (5,000 to 6,000 rpm for this motor) when the throttle control is set at "wide open". Too much pitch in the prop (or too much load in the boat!) overloads the motor causing overheating and extra wear.
 
Law/Seeker-

Larry has exactly defined "lugging". :thup

Marine outboards do continuous duty at relatively heavy loads compared to their automotive 4-stroke gas counterparts, and can't be lugged down like a brutish diesel motor.

Thanks, Larry :wink

Joe.
 
Larry and Joe - thanks for the explanation.

I have far more expeience with those "brutish" diesel motors than gasoline.

I've only been running outboards for 18 months. It is difficult for me to run an engine over 2000 rpm, because I'm familiar with diesel torque curves at rpm's, on trucks and heavy equipment.

I had a forest service ranger run my boat to find my WOT. It was 5800 rpm. Even though I was standing next to him I couldn't look at the tach, it was just so against my habits.

I have gotten used to running at 4500 rpm without to much dificulty now, but even my throttle backs off on it's own. I have to bump it back up to maintain those revs.

Do you guys know of links to outboard power curve/horse power/fuel consumption charts that I could look at?

Thanks Again,

Law
 
Seeker/Law-

Your question-

"Do you guys know of links to outboard power curve/horse power/fuel consumption charts that I could look at?"

If my memory serves me, I've NEVER seen one!

Often talked about, but never seen....

Seems there's a general agreement not to get into publishing that kind of data because of the kind of PR/adveretising battles that would result (?)

I have seen simulated curves in brochures, but they are without real data, and only suggest the relationship between rpm and torque, but no real numbers.

**********************

Good thing you're not driving a Formula 1 race car on the circuit at max of
19,000+ rpm!

Joe.
 
:smileo Hmmmmm...

Well the engines don't sound like they are lugging... and both tachs read about the same... is their an independent baseline tach that can be easily attached somewhere in order to check the helm tachs :?:

And gee... I gotta go back to school so I can re-learn math just to fully understand all those equations Joe wrote up :embarrased Thanx Joe. I am looking forward to fully understanding these figures. But it would appear that from the calculations I might be running 5K RPM and not the 4.5K that the tachs are showing. :disgust

Concerning the water speed, I just want to mention that I am reading it off a Lowrance 335 for both the GPS and the water speed indicator. But the water speed indicator is not a pitot tube it is a mechanical spin wheel. :crook

:teeth thanx again,
 
Ken-

Larry H would know for sure, but I'm guessing that an outboard mechanic would have a hand-held tach that could be used to verify engine/tach rpm.

I'm pretty sure we're right about the 5000 rpm being your current max, or at least something like that.

OK on the paddlewheels- most really good fishfinders have them. Probably more accurate than a pitot tube at higher speeds, and definitely more accurate a lower ones.

I wonder what others think about all this?

Joe.
 
Ken,
I remember Yellowstone John had a formula whereby you lost 3% of your horsepower for every 1000ft of altitude. If you're boating on Great Salt Lake you could expect a 10-12% loss over those sea level guys.
Les
 
Les-

Good point!

I think Larry H also said that it was -3% for every 1000 feet over the first 1000, if I'm not mistaken.

So an elevation of 4330 would be 3330 over 1000 ft, and

3.33 x 3% = 9.99% or 10% of your hp out the window!

This might account for maybe (guessing here) of 500 rpm lost on the top end?

Joe.
 
All,

On Yellowstone Lake in Yellowstone National Park we run max speed of 20 mph at 5000 rpm with propulse adjustable props set at one notch below normal marks used for adjusting pitch. This is the lowest setting possible. Elevation is approximately 8000 ft and I figured we lost 24% of our Honda twin 40's power. This is with a medium light load. Jo-Lee and I, full fuel and water, food and gear for a long weekend.

At sea level with heavy load cruising for extended period, adjust props two notches up with approximate top speed 24 mph at 5200 rpm. We live at 6200 ft. and most local outings are between 6000 and 8000 ft with a trip to the sea hopefully once a year. The propulse props have made things a lot easier for us.

Les, if the the 5000 rpm is correct and with that much weight up front the speed sounds about right to me. Agree that you do need to find out for sure about the rpm.

Jay
 
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