Double Eagle, center console.

Report the performance of your boat, supply as much information as possible (weight, HP, prop, speed, etc.).
Subject: Make the Glen-L design name the subject. If the design already has a posting, add your information to that post.

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FDMSIV
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Postby FDMSIV » Fri Dec 21, 2007 10:54 am

I agree with QC with respect to the bow plow. When the boat is on plane, the aft section of the bilge (at the drain) should have water (if there is water in the bilge). When planing the hull should be either flat, in which case the acceleration of the boat would move the water aft, or the boat should be slightly bow up, resulting in water moving aft.

It looks as though your boat is not getting completely on plane, which would explain why you always top out around 28 mph. Displacement/Semi displacement hulls are restricted to a certain speed, once that speed is reached, you could add infinite power and not increase the speed.

From the notes section of the Double Eagle also:
27 knots (*) (31 MPH) 150 SHP
31 knots (*) 200 SHP
(*) Attempting to obtain these speeds with the Inboard Version, due to the deep skeg, may cause excessive fuel consumption and may not be practical.


Also note here that the HP numbers are in SHP (Shaft Horse Power). This is b/w 10 to 15% of the BHP (Engine Horse Power) With a 135 HP engine, you are looking at b/w 120 to 115 SHP, which would also explain why you are getting about the same speed all the time.

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kens
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Postby kens » Fri Dec 21, 2007 3:55 pm

I did some more research, and fuel a run. Got fuel flow down to 5.1 gal/hr at 3000. I see that I would have to go diesel to get fuel to 3 gal/hr at 18kts, but doable.
If you figure 60hp @ 3000rpm; and 3000 is 66% of WOT rpm (4400), then the engine must not be even close to 140hp. More like 110 or 115.
I had a propshop run a program on my specs @112hp. He came back with 27mph swinging a 14x16 cup prop. That is about spot on to what I am really seeing on the water.
The boat IS up on plane though. No doubt about that. Check out the pic below of the wake thrown at 3000 cruise

I respectfully disagree with the prior post that semi-displacement hulls have a hull speed. That is not necessarily true.
Full disp. hulls do have a hull speed, yes.
Semi-disp hulls DO get up on plane if they are light, and have enough power. Once up on plane they CAN be driven faster. But in my case I can get up to 28mph and I run out of power to give. Put the perverbial 350Chevy in my boat and watch her fly!
I will concede though that my semi-disp form will not be as fast top end with that 350chevy, as a full-planing hull form.
But, the semi-disp form should be a better choice going offshore where sea conditions will likely dictate speeds at 15-20kts; or barely on plane.
These off-plane speeds is where the full planing hulls throw a trough of a wake with their transom squatting and the bow looking at the moon.
I think my next fuel consumption run will be testing an boat attitude to barely get bilge water to touch the garboard drains. Then record speed/fuel consumption at that hull attitude.

Image

QC
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Postby QC » Fri Dec 21, 2007 4:33 pm

kens,

Do a WOT run next time so that we have that fuel use. We can then determine if it is making full power. Anything over 10 GPH and I think it's doing what it should.

The method in which you arrived at 112 hp is flawed as the load goes up square of speed, or something like that, so fuel use is not linear with RPM . . . ;)

Also, I don't have much experience with inboards, but that inverse V wake in the middle tells me she is too far bow down. I get that when I run my trim tabs down hard . . . I still think you need more weight aft, not more weight, but some of what you got aft. Is there anything you can easily move?
If I had any dignity, that would've been humiliating - Adam from Mythbusters

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Dave Grason
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Postby Dave Grason » Fri Dec 21, 2007 5:37 pm

Uh Ken? .....ummm .....ummmm ....in that photo above, who's DRIVING the boat?
Isn't it amazing!! The person that never has the fortitude to pursue his own dreams, will be the first to try and discourage you from pursuing yours.

FDMSIV
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Postby FDMSIV » Fri Dec 21, 2007 5:39 pm

That is an awesome picture by the way!

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leakcheck
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Postby leakcheck » Fri Dec 21, 2007 6:17 pm

Dave, that is the first thing I thought too...when did they come out with autopilot? (actually they probably have them, but not for a boat that small perhaps)

Steve Gps Tracking, Loran dang..that would be neat

Shoot, sorry, that had nothing to do with Ken trying to get a half a mile an hour extra out of that puppy !!


Shoot dang, just buy a bigger motor !!

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kens
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Postby kens » Fri Dec 21, 2007 6:33 pm

Nobody is driving!
That came from the last newsletter Shop Talk: offset rudder.
One of the first things I noticed about this boat is it goes hands free.
It is dangerous at the same time too. You can walk around checking for leaks, loose hardware, flapping parts, status of cooler, etc., etc. All of a sudden there is a bend in the shoreline WhOOaaaaaaa!!
It must be the 'status of the beer cooler' that contributes to the 'bends in the shoreline'.

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Bill Edmundson
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Postby Bill Edmundson » Fri Dec 21, 2007 7:08 pm

Ken,

I'm looking at the wake, the way it tracks, and the size of the boat. Something is NOT wrong with this Boat!

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
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Postby QC » Fri Dec 21, 2007 7:50 pm

Ya know I have been noodling some more. A prop load "curve" IS relatively linear, so the fuel use should follow that as well. There is an efficiency issue though too, that is hard to grasp. Anyway, I want to think about the way that relates to your equation because idle speed matters too along with the recommended RPM range, which you are not getting to. So I don't believe that it is as simple as saying you will only make 112 bhp. I stil think 3.5 MPG is respectable for anything above 20 ft.
If I had any dignity, that would've been humiliating - Adam from Mythbusters

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kens
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Postby kens » Fri Dec 21, 2007 8:00 pm

I can get to rated RPM, but not with the size that the prop program sez I should, nor with the speed.
I agree that this boat aint doing too bad; but all the programs say it should do even better.
Even the Glen-L data in the plans say that. I am getting what the plans say........the plans say for the boat with full cabin and keel @ 4250lbs though.
I am by far more streamlined and nearly 2000lbs lighter.

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Postby QC » Sat Dec 22, 2007 9:33 am

Ken,

Can you post the plan data? I don't think that is online, at least I didn't see it first glance. If it says that a 4250 lb boat will use 3 gph at 18 knots with a gasoline anything, I have serious issues, even with a diesel . . . Yes diesels get better fuel efficiency and usually economy (depends on fuel price, purchase price etc.) but horsepower is horsepower and you simply can't make enough to cruise that boat on 3 GPH. I understand that you are considering that now as maybe unreasonable, but 5 GPH is good too. On top speed, most small I/O powered 17 ft. bowriders barley make 40 MPH with a 3.0. I owned one, I loved it, but that was a 17 footer with trim . . .

I also don't trust any programs, or mfr. test data. Merc's prop program rarely gets it right. We have compared that with hundreds of guys online at my other hang out (iboats), always off. My current boat was tested at 62 MPH with the same powerplant, same drive, same prop that I run. I have seen 57 twice, once was just this last Thanksgiving, I was running on fumes, no ice chest, no people (like your pic above), remote control, trimmed out as far as I could, not trim tab application. I could suck over 10 MPH out of her by driving the bow down with trim and tabs and leaving the throttle alone. Totally different animal, totally different hull, 320 bhp. But the point is trim matters a lot to all boats.

Also, look at the data for comp ski boats (direct drive). They are sticking 340+ bhp in those boats now and they still can't break 50 MPH. They used to use 230 or less and they got mid 40s. Another different animal, but there are definite design limitations inherent in hulls and powertrain combos as well.

I am a specs freak. I have been storing useless (until now) fuel economy and performance data in my head for 30 years. There are just no planing hull boats of the size that we are discussing that get over 4 MPG. There just aren't. Most of them in the 4250 lb. class struggle to get 3, at any point except hull speed. Also, I know of none that use a 3.0. Your boat frankly kicks ass as it is with a 3.0. You need to get the bow up just a little and then get the Rs in the correct band. That's when you will see maybe 2 more MPH . . . maybe 3 . . .
If I had any dignity, that would've been humiliating - Adam from Mythbusters

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kens
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Postby kens » Sat Dec 22, 2007 9:53 am

The online specs for the boat are 75hp @ 18kts. That is same info in the actual plans.
modern diesels can get 3gal/hr @ 75hp. Or so the power curves from Deere & Cummins & Westerbeke show.
I was hoping I could get my target numbers by streamlining & lightening the boat. Deleted cabin & keel is what I did.
I just wish I could verify what my 3.0L is truly making right now. I found 3 dyno shops close to home, but none go below 300hp.

QC
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Postby QC » Sat Dec 22, 2007 11:43 am

Yeah the very best diesels get around .3 lbs/ per bhp/hr . . . Which works out to around 3.2 gallons for 75 bhp. Don't forget you are using 50 year old gasoline technology, and I bet that it is in the realistic neighborhood of 10 - 12 bhp per gallon per hour as we used in the notes above. I just don't want you to chase something that isn't there. You are probably using that 60 bhp we talked about earlier and 5 gallons an hour to do that is good . . .

My guess is that it will make the bhp it is supposed to, and you could buy a lot of fuel for the price of a dyno run. This happens to be one of my favorite topics and my career, so that's why I am sticking with it. Good luck, I would beat this up just as much if it was me, it's easier to see the futility from the outside . . .
If I had any dignity, that would've been humiliating - Adam from Mythbusters

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kens
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Postby kens » Sat Dec 22, 2007 11:51 am

Do you know where I can get a carburetor wedge for the 2bbl Rochester? And the carb sits fore/aft on the manofold. My carb setting on slant may have a little effect.

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kens
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Postby kens » Tue Jan 01, 2008 4:21 pm

Made another fuel run today. Got a 'borrowed' prop from a shop in florida. They let me 'borrow' it as long as they charged my plastic card. So, I borrowed a 14.5x17 light cup. Runs good. awfully windy today, broke the 30mph barrier for the first time, downwind though. Noticed that at 3000-3200 cruise, water does in fact gather to the garboard drains, so there is no bow plow as previously mentioned. (at least not at cruise). The bow does lower, or, the transom rises, as I go up in RPM from cruise.
But I think the kicker is that I went out into the main body of the river today, in 22kt winds gusting to 40 and let her fly. Whitecaps everywhere, foaming building. She still got 21mph cruise @ 3150 in 3ft seas, with the occasional 5 footer thrown in. I tried her out real well and went WOT to the following sea, what a ride! Still got 28.5 mph and got airborne couple times, dried out the bottom a little and aired the prop. Still didnt slam though, just kinda settled back down into the water and kept moving on. I was most impressed. I turned around into the seas to go home and maintained cruise rpm & speed, very little if any at all penalty to go into the weather. Very impressive. After all this, I still got my 35minutes from 3gallons gas, and I made numerous brief runs WOT and also ran in that weather. This also had half my cooling water running overboard to dry out the exhaust a little, I think the lesser back pressure helped fuel consumption. The plans for this design say it takes the rough water, and it proved itself today. As I got back to the dock, a guy said Gale warnings just went out.
Maybe on a sane afternoon I can get 4 gal/hr and 20mph.


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