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Ken

Wax it and see what happens.

This not a work boat solution, just an interesting ?

Bill

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Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

I just installed a Northstar digital fuel monitoring gadget. I burned 3 gallons, and it said 3 gallons. Also my previous calculations were very close to the digital readout. My GPS died today, but I was indicating 5 gal hour at my previous 20mph. Showed nearly 8 gallons/hour WOT.
A bad day to do much figuring though, it was small craft asvisory. Seas 5-7 foot.

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God Bless our Troops; especially our Snipers

Kens how did the boat handle in the 5 to 7 foot seas. My Double Eagle will also be a center console. By the way I have been following your build and the information that you have shared has been very helpful. I will soon be posting pictures of my project.

The boat can take more than I can. Sunday was small craft warning, winds 20kts, she went right along, no pounding at all. Following seas were more treacherous than head seas this day. The following waves timing was nearly 1 boat length it seems, so there was bouyancy high on the freeboard at all times. Never took on water though. I wish I had a Youtube video of it, it was a wild ride. She was parting waves on the downwind run. Bow fully parting waves all the way up freeboard. I now see I can use spray rails at the sheer.
I think the engine in the center has everything to do with the handling. A outboard would squat at transom, and be light on the bow. As it is, wave action has to pick up most all of the boat at once in order to heave it. Even then, then its more of a even action.
At first I was concerned about the center console layout, omitting the cabin bulkhead at frame 5. She is solid as is. A solid stiff feeling build, even in this kind of weather.

_________________
God Bless our Troops; especially our Snipers

I been crunching some numbers on a re-power engine package. What I came up with is a eye-opener. If anyone has better info otherwise, please post a reply.
Currently my boat weighs 2480lbs with a 700lb 120hp cast iron engine. That engine has a VelvetDrive reduction gear on it, and so it came to the 700lbs. A cruise speed of 70% is 3000rpm @ 85hp. 2480lbs divided by 120hp=20.6 lbs per hp.

If I go with a 4BT Cummins 4cylinder diesel, it is 932lbs plus 62lb gear=994lbs.
WOT is 150hp/2800. Cruise is 2500rpm @ 130hp.

The 6BT Cummins 210hp is 1120lbs plus 97lb gear= 1217lbs. Cruise is 200hp @ 2000rpm.

With a 4-stroke outboard, I found 150hp, 466lbs (less prop) plus, a outboard bracket of 100lbs. This brings a outboard up to 575lbs. 70% cruise is 105hp. This works out to 15.7 lbs/HP.

Now crunch the numbers for a engine swap:
The 4BT diesel is a net increase of 294lbs & 30hp. Here I get 18.4 lbs/hp at WOT.
The ratio of HP to weight got better.

The 6BT is net increase of 517lbs & 90hp. Here I get 14.27 lbs/hp at WOT. The HP/weight ratio is even better. But look at the cruise, a whopping 200hp.

The outboard is decrease of weight by 125lbs & upped HP by 30 = 15.7 lbs/HP.
Cruise of 70% = 105hp.

Now check the cruise numbers and get shocked:
The current setup is 29lbs/HP
4-stroke outboard is 22.4/HP
4BT Cummins is at 21.3/HP
6BT Cummins is at 14.9/HP

So now, is a brand new outboard heavier than a cast iron diesel by seven lbs per HP?

_________________
God Bless our Troops; especially our Snipers

Don't know all that,but my 150 Mercury Optimax running a 16" pitch prop on a 21'wac runs out at about 45 on GPS at 5200RPM with a 18" pitch and light,it was running 5000RPM at about 50 MPH

The boat& motor and fuel weigh in around 3500-3800 LBS

Motor is on the transom too...no bracket with setback

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Boat building can best be defined as an endless series of
tragedies obscured by the occasional miracle, followed by a good bottle of beer.

Don't Dream Your Life, Live Your Dream

HUh????

I would think that the (somewhat dramatic) difference in figures is the cruising performance...check what percent of WOT power each engine does at cruise...

yours: 71%

4BT: 86%

6BT: 95%( )

outboard: 70%

actually, now that i look at the numbers, i cant help but ask where the HP@70% cruise was obtained...i assumed it was the output of the engine at 70% of max throttle (net fuel flow/consumption), but if the figures were calculated by simply taking 70 percent of the max(as is, perhaps coincidentally, the case for the current engine and outboard), then you may need to recheck your math ...either way, that 6 cyl diesel seems to cruise VERY effeciently...95% output at 70% fuel consumption almost makes you wonder why they bother with the extra 10HP at WOT...


just my 2 cents, hope that helps!
Denon

The unknown factor is at what rpm trims the boat at its opitimum angle to obtain the least amount of wetted bottom surface yet still can perform in a variety of conditions that creates the least amount of slippage for the hp. In some of the diesels, especially in the small turbo diesel engines, until you get the turbo cranked up, you do not get the rated hp either.


Wheels will give you several different readings too with the same motor. Sea conditions will also cause the boat to handle differently. You may not be able to run with an outboard as affectively and efficently like the inboard because of the different trim on the same bottom and the drag of the running gear too.

I went back to the beginning just now and found this post early on.

This is what I was talking about in my previous post. You may have a couple of issues. You maybe pushing too much boat in the water for sure. With a cupped wheel, your breakover is earlier. Find an incline meter and install it fore and aft along your covering board and see if you can get someone to take a couple of pictures. Try the boat at your 70 percent range and run a measured mile under the same conditions and check your speed. Then run your boat wide open and see what you get.

This is another post that screams out at me. You claim that your boat is faster in the chop.

Actually, I've seen that too. It puts a little air under the boat. The off-shore racers don't want it smooth. They run faster with a little chop. I guess the amount depends on the boat.

Bill

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Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

Denon:
I used 70% power as a cruise number for gas engines. The diesels I mentioned were used at their own rated power. The 4Bt Cummins is 150hp @ 2800 max; and 130hp @ 2500 continuos duty.

This model 6BT Cummins is 210hp @ max and 200hp continuos duty. This same basic engine is rated as high as 480hp max , and is known as pretty much 'bullit-proof' as high as 300hp. So, your right, that 200hp figure is about 95%, and even at 95% this engine is merely loafing along.

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God Bless our Troops; especially our Snipers

just an observation, but to perform the test accurately, shouldn't the rpm's all be the same for each test, then you would see the change in speed (MPH). The data doesn't show a constant, if your trying to gain max speed your constant would be rpm, speed is variable to prop pitch.

maybe i'm wrong, but thats what i see.

perform the test with the same rpm, and i bet your max speed changes substantially.

By the way i'm new here and hope i'm not out of line.

thanks

Terry

Yeah, there is a constant; the engine & the hull.
I am trying to get the most speed with the least fuel consumption.
Using a greater pitch prop increases slip, which negates the increased pitch.

_________________
God Bless our Troops; especially our Snipers