posted 12-05-2007 02:24 PM ET (US)        

I'm rebuilding a Yankee Voyager 20' and plan on getting rid of the old I/O in favor of an outboard. I was going to go with a 4-stoke but found a deal on a very clean 250 and am thinking I can buy an awful lot of gas for the $ difference. Only question I have is how much tankage I'm going to need to get any kind of range out of the boat.

posted 12-05-2007 04:10 PM ET (US)            

RPM GPH

1000 1.5 - 2
2000 4.5 - 5.5
3000 8 - 9
4000 12 - 13
5000 24 - 26
5500 26 - 27

I'll bet that at your typical cruise speed that the 250 OX 66 won't burn more than 2 and at maximum 3 GPH more than a 4-stroke or DFI 2-stroke of equivalent HP. 3 x $4.00/gallon is $12.00/hour more to run the 250 Ox66.

posted 12-05-2007 04:36 PM ET (US)            

On my 1997 21 Outrage, at cruise speeds 25-30 miles per hour, my fuel economy is typically around 2mpg, range 2-2.5mpg depending on conditions and load.

I went with the new EFI instead of a new DFI/4stroke because I got a deal also. I've burned about 2500 gallons over 300 hours since I have owned the engine. If I chose an engine that burned 30% less fuel, I'd have burned 750 less gallons. At $3.50 a gallon, savings over the 300 hours would have been about $2600.

The Optimax 225 or Yamaha 4 stroke 225 was about $4000 more to purchase at the time.

Rich

posted 12-06-2007 08:29 AM ET (US)            

If you don't believe that or the consumption rates noted above, then go look at performance reports at Yamaha. In particular, compare www.yamaha-motor.com/assets/products/otb/bulletins/ bulletin_otb_2StrokePerf_OX666_250hp_017-COB-Z.pdf (Note: Saltwater version) and www.yamaha-motor.com/assets/products/otb/bulletins/ bulletin_otb_2StrokePerf_OX666_250hp_01148-SKT-Z.pdf (Note: VMAX version which is tuned a little differently than Saltwater version). Both motors are in the 12 to 13 GPH range despite being on different boats. The only difference is that the Cobia achieves 31 MPH at 4000 RPM and the Skeeter is making nearly 50 MPH at 4000 RPM.

By the way, the fuel consumption numbers in that Cobia report are consistent with the numbers my friend sees on his calibrated NAVMAN F3100. His boat is a 4000 lb 24 foot cuddy cabin with a top speed of about 40 MPH.

With respect to a DFI or 4-stroke F250, 8 GPH at cruise is way too low. My own Ficht 225s burn 10 to 10.5 GPH each at 28/29 MPH cruise.

There are no corresponding Yamaha performance reports for the F250 4-stroke on identical boats (Yamaha has removed many of its Ox66 reports). However, these two are the closest performance reports that I could find is this one => www.yamaha-motor.com/assets/products/otb/bulletins/ bulletin_4stroke_hpv6_sws2_hyd-vector2200vx-f250txr.pdf and www.yamaha-motor.com/assets/products/otb/bulletins/ bulletin_4stroke_hpv6_sws2_pkr-2510wa-f250turd.pdf . Note that in both cases, the most efficient cruising speeds for the F250 (no matter what boat) occur between 4000 and 4500 RPM (about 67 to 72 percent of full throttle (just like the 2-stroke Ox66) and in that range the F250 is using fuel at a rate of 10 to 12 GPH, not 8 to 10 GPH.

As I said above, there is about a 2 to 3 GPH difference, at most, between an Ox66 250 and an F250 at cruise.

posted 12-06-2007 10:25 AM ET (US)            

Take two different boats. One is a planing boat that has a huge resistance at transition speeds, say 13-17 mph. It then gets over the "hump" and has less resistance for a while, then the resistance increases again. Assume it reaches top speed of 44 mph at an RPM of 5500 at full throttle (manifold pressure of 29 inches).

Boat 2 is a full displacement boat, where the resistance is more or less exponential with speed, without any inflection points. Boat 2 reaches full throttle at 5500 RPM (very different prop or gear of course) at 9 mph.

At 15 mph boat 1 will be at 3000 RPM, but its manifold pressure will be 27 inches, almost full throttle, to deliver sufficient torque to get over the high resistance of transition. Boat 2 at 3000 RPM is going, say 6 mph well down on the resistance curve, with MP of 20 inches. Much less fuel is burned at the same RPM.

Note the examples are fairly real life, though extreme because of the difference in boat types.

posted 12-06-2007 10:58 AM ET (US)            

Marine diesel manufacturers provide power/fuel curves for their engines. These power/fuel curves are independent of boat hull application. For them, load is load. If load X provides 6 MPH or 26 MPH, depending on application, the fuel consumed should be consistent with what the curve says for load X. When the same motor is propeller loaded the same even though on diferent boats, they will consume the same fuel, except for, perhaps, the transition zone to which no one is really worried about because no one strives to operate their boat in the transition zone.

posted 12-06-2007 01:37 PM ET (US)            

Redline on the Suzuki DF is 6000+ RPM. Redline on the Yamaha is 5500 RPM. That means that the Suzuki needs to turn faster to push the same boat the same speed as the Yamaha if it is propped to reach 6000 RPM at WOT like it should be.

Recall from the above performance report that the Yamaha 250 could push the Cobia 31 MPH at 4000 RPM (~12 GPH). If the Suzuki D250 was pushing the same Cobia boat 31 MPH it would be turning more than 4000 RPM and probably something closer to 4500 RPM.

posted 12-06-2007 02:17 PM ET (US)            

12.4 GPH at 4500 RPM ( www.suzukimarine.com/boat_builders/boat_tests/key_west_boats_inc/ keywest_225/df250/ ), or

12.25 GPH at 4500 RPM ( www.suzukimarine.com/boat_builders/boat_tests/carolina_skiff/ sea_chaser_2400_offshore/df250/ , or

12.5 GPH at 4500 RPM ( www.suzukimarine.com/boat_builders/boat_tests/carolina_skiff/ sea_chaser_250lx/df250/ ), or

11.8 GPH at 4500 RPM ( www.suzukimarine.com/boat_builders/boat_tests/ranger_boats/ ranger_2300_bay/df250/ ), or

12.1 GPH at 4500 RPM ( www.suzukimarine.com/boat_builders/boat_tests/mako_marine_intl_inc/ mako_232/df250/ )

posted 12-06-2007 11:45 PM ET (US)            

Thanks, everyone, for your responses. About what I expected. I used to have a Yamaha 225 Excel (carbs) on a Robalo 21 Cuddy, a very similar boat to the Voyager. That motor "exceled" at turning dead dinosaurs into noise. Even so, at 20 knots/medium load I'd get an honest 2MPG, if not better. Don't remember the exact RPM's but I think 37-3800. At 4000 the secondaries started opening and the burn rate went to about 35 gph-wot. I would expect at least as good from an injected motor with more advanced electronics on an almost identical boat.

If I was clocking tons of hours, Tohsgib's arguments would make sense, but I'm not. Assuming, in a really good year, I put 100 hrs at 20 knots on the boat. At 2 MPG that's (duh!) 1000 gallons, or $3250 at last summer's gas prices here. If the 4-stroke gets 3 mpg at the same speed, that's 667 gallons @ $2167 for a savings of $1083/yr. Add in $1000/year depreciation for the first few years and I'm looking at 15+/- years to recover the extra $10K for the new 4-stroke, not including dealer service costs, etc. Even if the fuel economy is twice as good, the payback still has to be 10 years.

Cooper and Peter both sort of hit the nail on the head without saying it. Stay off of the throttle, run the boat at a reasonable speed and the difference 2S vs.4S is negligible for the average user.

By the way, I have seen a displacement hull with outboards on it. Big, steel, trawler looking thing somebody obviously built in their back yard. About 50' LOA, 3 decks tall with slab sides, bluff bow and probably 16' beam. Had a pair of V-4's on a bracket welded to the transom. OUTSTANDING! I never saw it under way but it moved from Ft. Meyers, FL one winter to a canal in Punta Gorda the next. I bet the neighbors paid real close attention when that thing left the dock.

posted 12-07-2007 02:06 AM ET (US)            

I bought this one from the original owner right here in town. It's rotted under a tree in her yard for the last ten years. I've been trying to buy it from her since I was a kid. It's in pretty bad shape.

My understanding is that Bertram sold the molds for the 20' to Nauset Marine. They built the Voyager, or the hull at least, for Whaler. When Whaler gave it up, Nauset marketed (and still does) the boat as the Highliner 21. Or some history to that effect. There's a thread about it somewhere on this site.

I'm going with the outboard for 2 reasons. First, I hate outdrives. I always swore I'd never own one, then 3 years ago I bought a Tiara 20' and rebuilt it. Put in a fresh 350 Chevy with an Alpha. I know it's hard to argue with success, there's a bazillion of them out there, but always something wrong and what a pain to work on. All those gears, universals, gymbal bearings, rubber seals and boots..... I'll never own another one. Plus all that weight right in the butt of the boat and those dissimilar metals sitting in salt water all the time. Just inherently stupid, when you think about it. Second, experience. When I was in high school a buddy bought a Bertram 20 at a NOAA auction. We pulled the drive, glassed in the hole and hung a 200 Johnson on it. What a great boat. Unbelievable ride in a sea. He kept it for ten years and still regrets selling it. I don't think the vee on this one is quite as deep but it's pretty close. At the least, it's definitely got the Hunt look.

posted 12-07-2007 11:23 AM ET (US)            

quote:

---

That is the thirstiest outboard made sans V8 OMC's.

---

That is not at all accurate. Do you really believe the Ox66 burns more than a V6 Looper OMC OB?? I have owned two of these 250hp engines, and FWIW, on a 22' Whaler, on a whaler drive, I got 3mpg.

On my current boat, a 25' Parker, she runs around 4200RPM's, gets around 25mph and burns about 13 gph. This is measured by a calibrated Navman 2100. At 4500RPM's she will burn around 14-15gph. Running above that shows more fuel burn, but every OB is that way. Efficiency goes way down.

posted 12-07-2007 05:37 PM ET (US)            

I'm sorry, thought you were asking a question. Did they make a 250 hp V6 Looper OMC? John