Horsepower requirements for vintage Aquasports

[gran398]

The 19-1 Gull thread is fresh on our minds. The old photo illustrates  a 55 HP Evinrude Triumph.

The 19-6...many were delivered with a 3 cyl. 70 HP OMC. A higher option was an 85 four cylinder.... or the ultimate...a  115 OMC.

The first Aquasport, the 22-2 Flatback.  Contracted by the Bahamian government as an inshore patrol boat.  Designed to run twin 55 HP Homelites. 110 HP total.

It's replacement, the '73 and beyond 22-2 twelve degree. Still designated for twins, but as a single, ran a 135 Evinrude V-4 as top power option.

Point is, these boats were designed to get up quickly and run well with minimum horsepower...and weight. We've discussed it recently. The power/weight ratios/COG's were the same then as now. The formulas haven't changed, just add the setback for closed transom calculations.

 Raymond Hunt wrote the book on modern hull design.

Think we're missing the boat on classic hull design and performance.  Captain Matt dropped down in weight/HP with his 22-2 Flatback.  Kept close to  WOT speed while hauling on average the same customer load daily.

Propped right, same hole shot. But significant fuel savings.

Less may be more.

[Callyb]

We've discussed it recently. The power/weight ratios/COG's were the same then as now. The formulas haven't changed, just add the setback for closed transom calculations.

I may be off base here, but I believe I may have prompted parts of this post... Although the math may not have changed to calculate LCG and COB (COG's) a lot of us are doing modifications that add and subtract significant weight to the hull that may fall out of the original calculations for the original designed trim for the boat. Some of these may not be catastrophic or specifically dangerous, but result in a bunch of money and time spent to result in a rebuild that is disappointing in performance. Can some conditions be corrected by adding trim tabs, moving stuff around in the boat (ballast), etc? Sure, but why not figure out, reasonable close, what the expected trim and balance condition will be? I don't view this as being any different than any of us pointing out things like shoring and squaring the hull during a rebuild, or pointing out proper lamination schedules...

  I think this is a topic that needs to be tackled openly... I am not trying to say that everyone needs to calculate it down to the 16th  of an inch (or maybe a foot or so) or create a terror that really isn't there, but an individual going into these massive rebuild projects should be aware of the effects of trimming weight from the hull by using lighter materials, and then adding weights in places they were not imagined to be (ie; motor brackets, 4strokes motors, t-tops/towers, livewells, closed transom, etc.) and the dynamic effects on the boat from all of this. For example I have seen a lot of pictures of rebuilt flatbacks at rest that have a horrible trim, and ones that sit level and pretty. It is not to say that the ones that sit pretty were calculated, maybe some just got lucky, but I really doubt any professional builder is just totally winging it.

Then, the one question still remains, which I have seen asked a few times but never answered. Where is the designed/original LCG ar per the original design. This would be great to have as a reference for future rebuilds.

Not try to start a pissing match, just trying to spark a discussion that ends with some definitive answers.

     

[fitz73222]

Amen to that...

[seabob4]

Kinda like the old Buick GN.  The motor was capable (with no mods) of pushing the car to 150+.  But the body aerodynamics (or lack thereof) and suspension geometry dictated that the car wold most likely be dangerous at those speeds...so a governor limited the GN to 124 MPH.  

So power is one thing.  Useable power is another...

[gran398]

Exactly. These old flatbacks and twelve degree hulls weren't designed to run 55 mph. The idea was to provide an easy-planning, sweet running hull given the power available at that point in time.

The COG was mentioned since it has been discussed and is applicable. I too wish we had definitive numbers. Am sure they existed, but were lost long ago. Carl, you are on the right track with your estimates. Eugene stated there was a formula available, not sure where he obtained it however.

Couple of examples of how these boats run with what we consider low HP today. Skoot's 90 HP 19-6 easily ran in the mid twenties with 1000 ponds of men, gear, ice, beer, and food. My 22-2 planes and runs on a single 75 HP outboard.


Bottom line, these original designs run fine with moderate HP

[fitz73222]

Exactly. These old flatbacks and twelve degree hulls weren't designed to run 55. The idea was to provide an easy-planning, sweet running hull given the power available at that point in time.

The COG was mentioned since it has been discussed and is applicable. I too wish we had definitive numbers. Am sure they existed, but were lost long ago. Carl, you are on the right track with your estimates. Eugene stated there was a formula available, not sure where he obtained it however.

Couple of examples of how these boats run with what we consider low HP today. Skoot's 90 HP 19-6 easily ran in the mid twenties with 1000 ponds of men, gear, ice, beer, and food. My 22-2 planes and runs on a single 75 HP outboard.


Bottom line, these original designs run fine with moderate HP

What were your numbers running on one engine? RPM/speed? What was the load? I know what mine ran precisely with (1) 115 so I would like to compare.

[TheKid]

What were your numbers running on one engine? RPM/speed? What was the load? I know what mine ran precisely with (1) 115 so I would like to compare.

222FFV 140hp. 120 gal fuel, 40 gallon livewell, 3 MEN and 2 150qt coolers full of ice, 4500rpm = 19-21 mph

By myself with 40 gal fuel and 4 gallon livewell with 20lbs ice 4500rpm = 25-27mph

If you were asking...

I still want more power. Just found a 2000 Yamaha 200hp OX66 with 500 hrs that I am about to pull the trigger on.

[gran398]

Farley, not sure at present.

My neighbor was with me, we were taking it off the lift to put it on the trailer.

The starboard engine wouldn't idle down. Wouldn't run less than 2200 RPM. Turns out the  throttle cable at the helm for that engine had slipped loose from the set screw.

So went back to the lift, and he walked back to the truck to pull it.

Shut the starboard engine down. Then figured.... let's see if this thing will plane on one engine. So tilted the starboard engine up....and threw the pedal to the port engine.

She jumped right up  If had to guess, maybe she was running 23 mph? But not WOT....maybe 4600?

There was about 55 gallons of gas aboard. I'll get some accurate #'s this weekend and report back.

[Capt Matt]

High hp outboards and ping pong ball type scuppers are just a tempary band aid for a poorly thoughtout and incorrectly balanced build
No matter how much research and calculation we do while building until that boat is in the water and rigged there is always a little uncertainty that the floor drains will be above the waterline and she will ride just right. Luckily we have this resource to make the odds more in our favor. Trim tabs will make a stern heavy boat stop porpoising at the expense of burning more fuel but won't fix a bow heavy boat from bow steering. If all your calculations are close to right it takes almost no power to plane a flat bottomed boat.

We all seem to build theses boats into way more than they ever where designed to be. It's amazing to me that the flat back hulls designed almost 50yrs ago are versatile enough that they can support a full transom, towers, heavier motors and all the other crazy things we put on them. This design carries weight well so they equally make great mullet boats, crab boats etc

For the record my 150 four stroke burns more fuel than the 175 pro XS opti I was running. No outboard motor made burns as little fuel as a opti max period. Although it's only a gallon or so more on a 1/2 day trip, by the time I factor in the almost $5K a year in DFI oil I was buying it's pretty much a wash.

Knowing what I know now about the characteristic's of these flat back hulls anything over a 150hp is a waste. The sweet spot for cruising is 28-30mph no matter what size motor you run or how you trim her out.

Capt Matt

[fitz73222]

True words Matt,
Speaking for the 12 degree crowd from the early 70's 22-2's who actually rigged and test ran these boats from 74'-78' working for an AS dealer through high school and with my father owning two 22-2's, one CC and one FF that were new boats;I had a lot of time at the helm and I can share some real knowledge. First the self bailing issue; a brand new 22-2 would self bail at rest with twin 65 Evinrudes so +/- 500#. Two people standing at the transom would get your feet wet at rest. If you notice the details of these hulls, the drains were about 2" below the floor height for a reason. The reason was the so the rigging trough would drain. The bottom of the trough was about a 1/2 inch above the bottom of the scupper drains. So the Walt Walters 22-2 was designed this way at the insistance of having all surface water never entering the bilge. Short of a hull breach, the bilge stayed dry by design. To this day, 40 years later my 73' 22-2 has no bilge pump, with no original access. The only way water can enter the inner hull is through the bow mounted vents or through the exit vent on the port side. The vent system was a CG requirement when in 1972, manufacturers were required to ventilate below deck tanks. 1972 was the first year for 12 degree 22-2 with a below deck fuel tank.

The hull was designed for a single engine. The transom cut out for a 20" engine was 2" below the top of the transom. So for twins at a 26" standard spacing, it forced the rigger to bolt the engines on the lowest bolt hole on the inboard mounting side of the mounting brackets because of the cut out and would not allow for vertical adjustment to compensate for the deadrise change moving outward. Twins on these boats worked well but the optimum engine height was not obtainable. A single 135 on this boat was a pig for carrying a load. Twin 65's worked much better because they produced more static thrust with 6 cylinders (two three cylinder engines combined) instead of 4 for OMC V4. As Matt has suggested, 28-30 mph is a nice crusing speed for these hulls. So my comfortable crusing speed with twin 115's is the same as twin 65's of the day. My boat can be a chore to drive at 47mph with the 2X 115's and is not worth the fuel expense in the overall range. Not to say that trimming them out at WOT isn't a nice sound (like an MD-88 taking off!) Twin 75's are perfect for the 12 degree 22-2 for a combination of reasonable fuel consumption and nearly 40mph top end and sweet midrange at 4000 rpm's.

[gran398]

Agree with you both. Right at 29 mph is the sweet spot. Sounds good, easing along, run all day.

Maybe just a tad less for optimum cruising speed on the 170 and 19-6?

Hope the 240 owners will input their experiences as well.

[Callyb]

On my flatty, with the good old Black Max 150 and a 19" pitch prop and three people she cruised @ 28.7 GPS/3800 rpm, and W.O.T. @ 39.4 GPS/5500 rpm. Keep in mind this was bone stock and full of soaked foam. I really think a dry, stock flatback would be just fine with h.p. as low as a 90 horse. She was a little slow getting up on plane compared to what others report, but once she was up there you could roll the throttle back and she would sip gas. Before I pulled her apart I would regularly run 25-30 miles round trip to the fishing grounds and I don't think I ever used more than 7 gallons per trip. Can't complain about that.

I agree that a 150 is going to be plenty, even with a heavy rebuild.

[gran398]

Exactly. These old flatbacks and twelve degree hulls weren't designed to run 55. The idea was to provide an easy-planning, sweet running hull given the power available at that point in time.

The COG was mentioned since it has been discussed and is applicable. I too wish we had definitive numbers. Am sure they existed, but were lost long ago. Carl, you are on the right track with your estimates. Eugene stated there was a formula available, not sure where he obtained it however.

Couple of examples of how these boats run with what we consider low HP today. Skoot's 90 HP 19-6 easily ran in the mid twenties with 1000 ponds of men, gear, ice, beer, and food. My 22-2 planes and runs on a single 75 HP outboard.


Bottom line, these original designs run fine with moderate HP

What were your numbers running on one engine? RPM/speed? What was the load? I know what mine ran precisely with (1) 115 so I would like to compare.

Single '03 75 HP Merc 2 stroke, 1973 22-2 Aquasport, starboard engine raised:

25.8-26.0 mph on the GPS, 5100 RPM. 65 gallons fuel, 440 pounds of crew, no wind.

Captain John was aboard and took the #'s.

[GoneFission]

Single '03 75 HP Merc 2 stroke, 1973 22-2 Aquasport, starboard engine raised:
25.8-26.0 mph on the GPS, 5100 RPM. 65 gallons fuel, 440 pounds of crew, no wind.
Captain John was aboard and took the #'s.

Yep - saw it - 26 MPH on a single 75 at 5100.  She might have done a little more trimmed out.     Pretty impressive.  Scott's running an 18 pitch prop on these motas, which seems about right.  Scott's boat runs well and is solid as a rock.  And those twin 75s sound great when you wind them up a bit.  It's music to a gearhead's ears!  

[Necessary Evil]

I am wild about the performance of my 1976 12 degree 22-2 with the Suzuki DF175, but I am sure 150 would have been plenty. I am firmly convinced that putting a heavy V6 on these hulls is a mistake. My boat self drains at rest, even with the motor hanging out 18" on a Porta Bracket. It is so well balanced under way that it seems totally indifferent to heavy loads; my performance numbers hardly change with heavy vs. light. I put trim tabs on, and I love them, but they are not absolutely necessary.

I mostly cruise around at about 25 kts, and I get about 4 NM/gal. with a light load. WOT is 34.5 kts and drinking fuel at 17.7 gph, so nearly 2 NM/gal even at WFO. And I gotta tell ya, the sound that Suzy makes as she revs up to 6100 is pretty darn cool! Worth a few extra gallons from time to time!

Bottom line, with a lot of very helpful advice from people on this forum, I really think my set up is about perfect! Thanks CAer's :)