Seafari 25 performance

[cdavisdb]

Well, I finally got my new (to me) boat back from the mechanic. Looks like the work was done well, but it took a loooonnnggg time. First time out today and I did a bunch of performance testing, results below. You guys who are familiar with vacuum gauges, please look at my results and tell me what you think. I'm particularly interested in using it to help establish the most efficient cruising speed. (sorry for the rough tables, I can't get this program to work quite right)

The boat is a near original 1972 25 seafari with a 1998 fuel injected 5.7GSI volvo/volvo sx duoprop. aluminum D2 props that were somewhat nicked when I started and are a lot nicked now. Somebody put a sand bar where it wasn't supposed to be. The grounding only affected the fuel economy estimate and probably not much of that.

I suspected the boat was underproped. It is. max rpm is 5100, 100 over the max. My old Seabird 24, about the same weight,carborated 5.7/290 duoprop with F5 stainless props, was right on red line for that engine, 4600 rpm. This engine has a 4600-5000 max rpm range. If I go to stainless props that drop the rpm to 4800, do you think I will gain a knot or two and fuel economy to get near 2.9 npg from the current 2.6?

Conditions, 15 knots out of the NW, long fetch in a shallow bay and a short, breaking 1-2 ft chop, the kind I like to call "washboard" Not a major test for the hull, but I could run straight into it at 28 knots and still be comfortable. No pounding, the hull just got jittery sometimes. My old seabird would have been rattling my teeth at anywhere near that speed.

General impression: I'm going to like this boat. It obviously is going to live up to its rep as a sea boat. Its tippy, much more so that my seabird, but no worse than a formula 23. It is very lively at rest, I think more weight will help that as it settles down on its lines. Did not see a snap roll like a formula, but the conditions were not a fair test. Too early to tell on roll.
Just looking at the hull, it doesn't have the appearance of a dry boat, but I ran around for 3 hours on a day that should have produced a fair amount of spray and had almost entirely dry decks and very little spray on the windshield, not a complete test, but looks good.

24 mile economy run, 2.6 npg Half way through, props very nicked. One person, full load of fuel, 3300 rpm. Can anyone tell me what is the most efficient rpm for a fuel injected engine?

hole shot: just over 2 seconds

All other speed/vacuum data taken with one person, 1/2 load of fuel

NO LOAD, OUT OF GEAR, WARMING UP
RPM Vacuum
500 13
1000 16
1500 19.5
2000 20
2500 20
3000 11
3200 9
3600
3800 6
4000 4

Under LOAD

falls off a plane below 2400 if tabs and drive are not down. Minimum planing speed, 12 knots at 2200..

RPM Speed Vacuum
2200 2200 --12.2, tabs down
2400 --14.4 tabs down
2400 --13.2 tabs up
2600 --15.7
2800 --18.3
3000 --21 --12
3200 --23.6 --10.5
3400 --26 --9
3600 --28.2 --9
3800 --30.2
3900 -------7
4000 -------6
4200 -------5
4350 -------4

[McGillicuddy]

Sweet! Congrats! Gets some pics up. Nice report. I think you'll be right on target with your stainless decision. I'm a bit curious myself. I'm sure Bushwacker will chime in re. vacuum. If I'm not mistaken he's a proponent of such measurement to maximize performance and warn of impending doom
Impressive min. planing speed...
Your economy on the seafaring hulk is impressive, too - if you can pull 3mpg out of her I'll be upgrading sooner than I suspected. Love to hear more about rock and roll troll and drifting or sitting in swells.

I'm not familiar with variability of prop geometry on duoprops so your experience will be enlightening... please keep us posted.

PS you didn't buy the one in LA did you?

[cdavisdb]

I got lucky. This one was close to home, in Palm Beach Gardens.

[76Red18]

Cool!! The lack of spray doesn't suprise me. I like that 12 knot min planing speed also. That comes in handy offshore.

[Bushwacker]

Offhand I'd say that's pretty good performance for a hull with that much deadrise with a set of nicked up props! Very impressive that you can plane at 12 mph, as many boats with 25 degrees of deadrise can't do that! I always thought that hull might need a big block engine for good performance, but that small block/duoprop setup is lighter and very efficient, so it sounds like it's a good match. By the way a friend of mine named Herman Johnson had a Seafari 25 and lived in Palm Beach Gardens - any chance you bought his boat?! We must live pretty close; we ought to get together some time!

I'd take those props to Bobby Soles and ask his advice; he might be able add some more cup to them to get the rpm down. Best to tweak them to determine right dia/pitch before you spend big $ on a stainless set! You might also want to keep that aluminum set, as they sound ideal for heavy loads. As Fr. Frank says, most folks end up over propped because they don't test the boats with the loads they finally end up running! 5100 doesn't sound like a lot of rpm for a small block Chevy, but maybe they're worried about the valve train. Those ball-stud rockers with the pressed in studs are the first thing most guys change when they try to soup up a Chevy.

Vacuum numbers with no load on engine aren't particularly meaningful. Main thing is that vacuum is steady at idle; 13" at idle sounds a little low, but that's a function of cam lift, duration and overlap. The fact that vacuum picks up so much at 1000-1500 is further indication of fairly aggressive cam timing. The 5.2L in my truck runs about 19" at about 600 rpm idle, but it's only 235 hp with a very mild stock smog motor cam.

The only comparison I can give you on speed/vacuum is from the "Unohu", a friends old SeaCraft 21 when it had a carbed Mercruiser 350 Chevy/Alpha 1 outdrive. I believe it was rated at about 260 hp with the gear ratio he was running. He used to cruise at 20 kts/~23 mph at about 9" vacuum (with very heavy Bahamas-cruising type load), and I believe top end was around 45-47 mph; used to average about 2.5 mpg. I think you're doing quite a bit better than that! He later had a carbed Volvo (non-duoprop)/350 Chev in it rated at 270 hp, and he claimed it would run 50 mph, but I believe it was jetted richer and he indicated he lost some mpg.

Regarding optimum cruise rpm, IC engines are generally most efficient, as indicated by minimum specific fuel consumption (fuel flow/HP), at the point of maximum torque. If you can find out the max torque/rpm rating that would be a starting point. Maximum mpg of the installed engine/outdrive is a little different and involves a lot more variables. Installing a flowmeter is the best way to nail down optimum cruise settings; the modern systems that combine speed with fuel flow with speed will calculate instantaneous mpg and can even help you optimize engine trim and trim tab settings, in addition to tracking total fuel burn. The next best way might be to look carefully at the vacuum/speed relationship. I'd suggest plotting vacuum vs. speed and then looking at inflection points on the curve, after you're up on plane. You're looking for the combination of highest speed/highest vacuum. Large speed increases with a small vacuum drop indicates you're in the optimum speed range. When vacuum starts dropping faster than speed is increasing, then you're running faster than optimum. (Caution: this approach is only valid above about 5" vacuum; on most engines the carb or FI system will dramatically increase fuel/air ratio or richen the mixture at or below 5", so you'll see big increases in power and speed for small decreases in vacuum once you get below 5". Part of this increased fuel flow is to help cool the exhaust valves, because lean mixtures burn very hot!)
Denny

[seafari25]

Connor,

Glad to see you got her wet!

Your performance numbers are not too far off of mine. Those duoprops got me beat by a few MPH. Pretty much, where you indicate your speed in knots, I get the same in MPH only my max RPM is 4200 @ 32MPH.

Running into a chop, I find it best to trim bow all the way down for the most comfortable ride. As far as spray, I usually manipulate the tabs so as not to create any. In really nasty conditions, I may get a little over the rear quarter but I'm not sitting back there. If I'm travelling a long distance in those conditions, with passengers back there, I'll put on the rear curtains for a completely dry ride.

You've got yourself a nice rig there. ENJOY! Ours is being pulled this week for the winter so the next 6 months are going to be long ones for me...

Brandon

[cdavisdb]

Wow Denny, that's fabulous information. Thank you VERY much!

It looks like I can adjust rpm for max efficiency on the fly with a vac gauge, no matter the load.
Looks like 9 inches is near the magic number for me too, about 35-3600 with this load. Bahama trips are my main use of the boat and that means about 1000 lb over what I was carrying yesterday. I'm a little surprised the rpm for high efficiency is above 3400. That seems high to me, a lot higher than a carbed 5.7. Is that a function of fuel injection? Maybe that will change with higher load. One more question on vacuum guages: This one is on the end of what must be 25 ft of plastic hose. Does hose length affect reading?

The low planing speed hasbeen a huge advantage for me, although with the seafari, I won't need it as much. It is mostly the result of the duoprop, but my seabird would plane down to 11 knots, even with a heavy load. It had very wide tabs, which I liked a lot, and they may have had something to do with the low speed. I really hate the single stick control on the seafari tabs and will be changing to a two button soon. Also maybe wider tabs, when my budget recovers a bit.

On props, I will be getting another set, as soon as I figure out what size, and use these as a spare. My wallet howls every time I think about stainless volvo, but I run in shallow water, coral, etc a lot. Think I gotta do it.

Has anybody tried putting extra weight, lead, concrete, whatever, way up in the bow of this boat? The engine sits so low, 3-4 inches below what volvo recommends, that I worry about water intrusion, especially with the idiotic volvo placement of the flapper valves inside(inaccessible)the exhaust pipe. You can't tell if they are working or not. Mine were stuck when I bought it. I'm planning to install 2 inch spacers to raise the risers, but when 3 or 4 guys gather in the stern, the boat sits very very deep. Maybe a couple of hundred lbs in the bow would help keep the stern from sinking so far. Might also damp the roll a little.

Thanks again.

[cdavisdb]

Denny, this was not your buddies boat, but you have probably seen it, pretty distinctive, light blue hull, white topsides and bimini, white fish box built out aft of and across the stern.

Brandon, what width tabs do you have on yours?

Connor

[Bushwacker]

Hi Connor,

If you're gonna carry another 1000 lbs, which sounds typical of Bahama trips, the props you have may be about right! I had my spare Al prop cupped so that it would turn about same rpm as my stainless prop; when I got over to the Abaco's I would switch my good stainless prop for the aluminum prop to prevent reef rash on my get-home prop!

The rpm for peak efficiency is primarily a function of the cam but the amount of gear reduction and prop design will also affect it. A 4 blade prop will sometimes be more efficient at cruise because it has less slippage, but higher friction losses at high rpm tend to hurt top speed. The duoprop may have similar issues, but it should eliminate all the swirl in the prop wash which should be a good thing.

Both the diameter and length of the tubing will affect TRANSIENT response of any pressure gage, but since there is no flow going thru the line at steady state conditions, it won't affect the reading. When I first hooked up the vacuum gage in my truck, I tee'd into the vacuum line running to the power brake booster with a 1/4" line about 2' long and that was too sensitive - the gage would fluctuate a couple inches as each cylinder fired! Had to put a .060" dia. orifice in the line to stop that!

Sounds like you might want to move those exhaust risers up more than a couple of inches! Having them too low is a quick way to kill an engine! I'd never add weight to a boat just to balance it, but have you considered adding a ballast tank? It would damp roll as well as help adjust longitudinal trim. (Check out Moesly's patent Moesly's Patent on Carla's web site.) He used ballast tanks in the race boats; they worked well and he supposedly designed the Seafari 25 with the idea of using a ballast tank, but sold the company to Potter before he ever built a 25 and Potter evidently never included the ballast tank.
Denny

[seafari25]

I guess a picture is worth a thousand words. This was taken before my cleanup and paint a few years ago.
[image][/image]

I credit my Grandfather for getting those on. I've never run the boat without the plates on the tabs but they are super sensitive when activated. I usually have a list corrected seconds before the weight shift In my younger, crazier, foolish, stupid, stupid, stupid years, usually to impress a young lady...stupid...I would trim port tab all the way down and starboard up and lay the boat on her side, without turning the wheel, at about 20 plus and yell" we're goin over" or some stupid thing like that...anyway my point is, the tabs are effective and...we were all young at some point . Ours are made of steel and are holding up but when I have to replace them, I'll try aluminum.

Well...I guess I gave you a thousand words anyway