run it like a trawler ????

k9th · Post by **k9th** » Sat Mar 31, 2012 10:07 am

Most of the fishing charters at our marina are gas with carbs and troll for hours at just below 2kts for salmon. I do the same with SeaDog and have had no issues with the plugs fouling or the engines loading up. Every now and again I will pop one out of gear and throttle up to about 2,000 for a few seconds and back down and then do the other one too.

DOUBLE R · Post by **DOUBLE R** » Sat Mar 31, 2012 10:34 am

Max hull speed may not be the most fuel efficient. Many times on semi-displacement hulls max economy can be at or near dead idle. As with air, Water resistance is not a linear progression but rather a geometric function.

summer storm · Post by **summer storm** » Sat Mar 31, 2012 11:27 am

Ever since I read the "How many Hours will you run your boat this year" post I've been running my fuel burn numbers and to be honest I don't like what I see. I think if it stays around 5 per gallon I'm OK but if it goes much higher I'll be in low speed mode for a while. Next step, putting a couple of 165's in the boat!

kevinz · Post by **kevinz** » Sat Mar 31, 2012 8:50 pm

I have Crusader 454xl's. No fuel injection. On plane at 3200-3400 RPMs, (24MPH) my Garmin fuel flo screen says I'm burning 26 GPH. At 1500 RPM's (8MPH) towing the J-14 Skiff, the Garmin says fuel burn is 6 GPH. I like the slow speed, half the fun is getting there!! IF... the slow speed don't cause me headaches!

Paul · Post by **Paul** » Sat Mar 31, 2012 8:51 pm

One thing to keep in mind if you choose to run in the 1000 RPM range with a Velvet Drive that the clutches tend to slip a little at such a low RMP. This will result in reduced clutch plate life expectancy. Shops that service these transmissions see this effect mostly on vessels that use the main engine for trolling.

Big D · Post by **Big D** » Sat Mar 31, 2012 9:25 pm

Good point Paul, that's pretty much boarderline rpm while still trying to maximize clutch longevity.

jimbo36 · Post by **jimbo36** » Sat Mar 31, 2012 10:19 pm

kevinz, so you are saying that a 24 mile trip will cost you an additional 8 gals of fuel running @ 3200-3400 RPM. Is this your sweet spot on plane? by the way your boat looks great on plane on your avatar.

jimbo36 · Post by **jimbo36** » Sat Mar 31, 2012 10:20 pm

kevinz, so you are saying that a 24 mile trip will cost you an additional 8 gals of fuel running @ 3200-3400 RPM. Is this your sweet spot on plane? by the way your boat looks great on plane on your avatar.

gruhs · Post by **gruhs** » Sat Mar 31, 2012 10:54 pm

k9th wrote:
captainmaniac wrote:Only if you are running at or below 'hull speed' (= 1.34 x square root(water line length)). That is as fast as you can push through water without the boat trying to climb on top of it (ie plane). Hull speed is the fastest you can go without starting to burn power trying to also lift.

I don't have the number near me, but for the F32 waterline length is about 28' I think. So about 7 knots (around 1500 rpm probably) is going to be the fastest you can go for the least fuel.
Good point and thanks for bringing it up.

Has someone calculated what the hull speed is for the tri-cabin using the
formula? (I don't know what the length at water line is)

k9th · Post by **k9th** » Sat Mar 31, 2012 11:27 pm

gruhs wrote:
k9th wrote:
captainmaniac wrote:Only if you are running at or below 'hull speed' (= 1.34 x square root(water line length)). That is as fast as you can push through water without the boat trying to climb on top of it (ie plane). Hull speed is the fastest you can go without starting to burn power trying to also lift.

I don't have the number near me, but for the F32 waterline length is about 28' I think. So about 7 knots (around 1500 rpm probably) is going to be the fastest you can go for the least fuel.
Good point and thanks for bringing it up.
Has someone calculated what the hull speed is for the tri-cabin using the
formula? (I don't know what the length at water line is)

The formula, according to Wikipedia, allows a range for the first factor which was given here as 1.34. It can range between 1.34 & 1.51. The 1.34 is the conservative value. I estimated the water line length at 32ft based on my trip to the boat last weekend. Doing the math gives a speed range of 7.5 - 8.5 kts using the 1.34 - 1.51 factor. Not sure what RPM that would be. Been wondering also with the bottom exhaust pushing the hull up, how much of a factor that will be. I don't have to go very fast at all till I'm on plane.

gruhs · Post by **gruhs** » Sun Apr 01, 2012 10:08 am

good morning K9th...
That's my favorite speed for easy afternoon for cruising... as I recall that
would be about 15-1600 rpm for me. By the way if we meet up on the lake
somewhere this season, we just finished changing the name of the boat.
The old name wasn't chosen by us, it just came with the boat and now it
carries the name of one of our first boats years ago.

k9th · Post by **k9th** » Sun Apr 01, 2012 10:40 am

That's about what I thought on the RPM.

Name looks nice Gary, glad you got it changed. See you soon.

gettaway · Post by **gettaway** » Sun Apr 01, 2012 12:03 pm

As most of you know I repowered this past year to GM / Mercruiser inline 6 six cylinder, 165 hp engines. Same ratio transmissions 1.52 to 1, and same 3 blade 16 X 15 bronze props.

I am running at just 9-10 knots and burning 3 gallons an hour. For me the trip is the best part

its working for me and with the price of fuel its even better, I ended up with a neat engine room as well

gruhs · Post by **gruhs** » Sun Apr 01, 2012 12:19 pm

wow, you could eat dinner in the that engine room. Very, very, nice,, wish mine looked that fresh and clean

Gary

k9th · Post by **k9th** » Sun Apr 01, 2012 4:03 pm

gruhs wrote:wow, you could eat dinner in the that engine room. Very, very, nice,, wish mine looked that fresh and clean

Gary

You going to change the boat name on your signature?