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With mast and ballast , at 2000 rpm and no strong head current , we get about 5mph and 10mpg . Go to 3000 and the mpg drops to 6mpg while the speed only increases about 2mph .

When I lose the mast and ballast , I was hoping for about 7mph at 2000 rpm , what you guys think ?

Three Gypsies wrote:With mast and ballast , at 2000 rpm and no strong head current , we get about 5mph and 10mpg . Go to 3000 and the mpg drops to 6mpg while the speed only increases about 2mph .

When I lose the mast and ballast , I was hoping for about 7mph at 2000 rpm , what you guys think ?

What is your max rpm without mast/ballst? You might be able to re-prop to a higher pitch.

Bob

Three Gypsies wrote:With mast and ballast , at 2000 rpm and no strong head current , we get about 5mph and 10mpg . Go to 3000 and the mpg drops to 6mpg while the speed only increases about 2mph .

When I lose the mast and ballast , I was hoping for about 7mph at 2000 rpm , what you guys think ?

Not going to happen. You'll see little to no measurable difference at these speeds. The decrease in fuel efficiency is caused by the bow wave you're making at 7mph, not so much by weight. Dumping ballast helps while semi-planing, but not in displacement mode.

You are almost correct . I find cruiseing at 3000 rpms @ 7 mph on my 50 hp Merc. in no current is what I want. Burns 5.2 mpg.
At 2000 rpms I get 10.5 mpg.@ 5.1 mph.
At 2500 rpms I get 5.9 mph and burn 8mpg. and this I use most of the time on long distance of round trip of 80miles or so on twin 6 gal. tanks.
So double the fuel 2mph faster.
Makes sence to do 5.1 mph and get much better range but some of us like the extra 1mph faster. If in a real hurry I can do 17mph and burn the tank dry in less than 1 hr.Thats only going to happen if out running a thunderstorm or emergency on the boat or empty the ballast.
That's with no wind.
Dave

Three Gypsies wrote:With mast and ballast , at 2000 rpm and no strong head current , we get about 5mph and 10mpg . Go to 3000 and the mpg drops to 6mpg while the speed only increases about 2mph .

When I lose the mast and ballast , I was hoping for about 7mph at 2000 rpm , what you guys think ?

Since I have no problem getting to my redline of 6000 rpm , perhaps I should go up a pitch on my propeller ?
Would that increase my speed at 2000 rpm without increasing my fuel burn ?
Planning the boat is not something I am interested in . The only way I would ever run the boat over 10mph is because I am rushing somebody to a hospital .

Three Gypsies wrote:Since I have no problem getting to my redline of 6000 rpm , perhaps I should go up a pitch on my propeller ?
Would that increase my speed at 2000 rpm without increasing my fuel burn ?
Planning the boat is not something I am interested in . The only way I would ever run the boat over 10mph is because I am rushing somebody to a hospital .

1 pitch = 2-300 rpm depending on HP--6,000r's is in the way high upper end of most engines. A good prop shop should let you test their prop. What engine do you have? Sea level?

Bob

bscott wrote:

Three Gypsies wrote:Since I have no problem getting to my redline of 6000 rpm , perhaps I should go up a pitch on my propeller ?
Would that increase my speed at 2000 rpm without increasing my fuel burn ?
Planning the boat is not something I am interested in . The only way I would ever run the boat over 10mph is because I am rushing somebody to a hospital .

1 pitch = 2-300 rpm depending on HP--6,000r's is in the way high upper end of most engines. A good prop shop should let you test their prop. What engine do you have? Sea level?

Bob

We have a Honda BF50 . Looking for a good trawler speed/ good gas mileage , prop pitch . I understand if you can't reach redline then its to much pitch and the motor is overloaded . Like starting a car off in third gear .

Usually there is a top RPM range ie 5500 to 6000 rpm with your average load. If you are hitting 6000 then you have room to repitch to 5000. I don't know much about HONDA 50 but you might be able to borrow a higher pitch prop from a local prop shop starting with 2 pitches higher. A 50hp might not have great hole shot with the higher pitch but it mingt get you 6knts at 2000.

Check your bottom paint--lots of affect on speed.

Bob

bscott wrote:Usually there is a top RPM range ie 5500 to 6000 rpm with your average load. If you are hitting 6000 then you have room to repitch to 5000. I don't know much about HONDA 50 but you might be able to borrow a higher pitch prop from a local prop shop starting with 2 pitches higher. A 50hp might not have great hole shot with the higher pitch but it mingt get you 6knts at 2000.

Check your bottom paint--lots of affect on speed.

Bob

Thanks , I am going to try two more pitches . I am running a 12 Michigan wheel , right now , will go to a 14 .
Our Gypsy's bottom is very dirty , right now , she has been a float for nearly two years and been 5000 miles when we finish this cruise.
The figures I was giving are from when she was clean .

Three Gypsies wrote:

bscott wrote:Usually there is a top RPM range ie 5500 to 6000 rpm with your average load. If you are hitting 6000 then you have room to repitch to 5000. I don't know much about HONDA 50 but you might be able to borrow a higher pitch prop from a local prop shop starting with 2 pitches higher. A 50hp might not have great hole shot with the higher pitch but it mingt get you 6knts at 2000.

Check your bottom paint--lots of affect on speed.

Bob

Thanks , I am going to try two more pitches . I am running a 12 Michigan wheel , right now , will go to a 14 .
Our Gypsy's bottom is very dirty , right now , she has been a float for nearly two years and been 5000 miles when we finish this cruise.
The figures I was giving are from when she was clean .

I took the Gypsy out yesterday and ran WOT upstream and down . I was only able to get to 5100 rpm , with a redline of 6000
When the boat bottom was clean and she was lightly loaded , I could easily hit 6000rpm , but now with the boat loaded for living aboard and her hull having barnacles , its harder to push her thru the water .
The boat will be coming out and her bottom cleaned . The mast is coming off and the ballast dumped . But she will still carry a heavy load because when we cruise its for months at a time .

LOOKING for advice ,,, I am currently running a 12 pitch Michigan Wheel , thinking about changing to a 14 pitch . Do you guys think this is a good idea ? Or do you think its to much ? As stated , I am looking for a faster trawler speed and good gas mileage . Not interested in trying to plane her .

We have converted 'Stirling' to a Trawler for this season. only been out once so far, but we have certainly found that we don't need the ballast filled (she is brilliantly stable, although you have take a bit more care in balancing the loading. We got up to 6-7 knots for about 2500RPM on our Tohatsu 50D2 have not measured fuel consumption against distance yet, but last year (with mast & ballast) it took 3500RPM to achieve that speed, so I am expecting good news on that front. I did try filling ballast to see what it added in stability and I think I would be happier with it filled if it was a bit rough, but its fine empty in lighter seas.

I enjoyed the first day so much, that I am thinking I might just make the conversion permanent, thinking of installing a couple of seats either side of the companionway, moving steering and controls up there, remove the pedestal, and put some kind of fixed pilothouse over the forward half of the cockpit. Remove the rear seat, replace it with a bulkhead (where the back of the seat was), would lose a bit of cockpit but not that much.

Any thoughts.... even if you think it's heresy

John -

I've had exact same thoughts on that mod, tho I'd really miss the sailing aspect. However, an extension of the idea would be to install a tabernacle mast base to such a height that the mast, when hotizontal, would easily carry on top of the pilothouse.

Oh great! Now I'm really thinking about it!!!...

JohnCFI wrote:We have converted 'Stirling' to a Trawler for this season. only been out once so far, but we have certainly found that we don't need the ballast filled (she is brilliantly stable, although you have take a bit more care in balancing the loading. We got up to 6-7 knots for about 2500RPM on our Tohatsu 50D2 have not measured fuel consumption against distance yet, but last year (with mast & ballast) it took 3500RPM to achieve that speed, so I am expecting good news on that front. I did try filling ballast to see what it added in stability and I think I would be happier with it filled if it was a bit rough, but its fine empty in lighter seas. ....
Any thoughts.... even if you think it's heresy

No heresy in my view! Your observations above are consistent with my overall impression. On our coast most sailboats run with bare masts most of the time (local fishermen call them "stick boats" for that reason). I like the clear decks, simplicity, and low wind-resistance experienced when the mast&rigging are back home. As has been noted on this site, running at say 2-3 mph the rpm seem not to be affected much by ballast-in-or-out (at least on flattish water). It suddenly struck me at the end of last season though that perhaps the engine was quieter with ballast in ... and that maybe this was to be expected if the outboard exhaust was deeper beneath the surface: must remember to experiment with this in future for quiet low-speed poking along the coast. I don't think I have the imagination to put a pilothouse on Kittiwake, but for ocean running in less-than-ideal conditions I could see it being of interest.
Kittiwake

Well, I broached the subject with the admiral, and her only comment was 'we could take it out more if you were not always at the back on your own in the wet'. Surely that is permission to go ahead to the full planning stage, with implementation over winter (for us that's next April/May, which gives time to plan and acquire the necessary bits and bobs for the job)..

Keep us posted with your plans!

Here's what I'd do...

1) Remove rudders, pedestal, and helm entirely and plate over the cockpit hole. Then put teak decking over the cockpit. Leave all the fiddly bits so they can be replaced when you sell.

2) Go to Baystar hydraulic system on the o/b, with the helm moved to either the port or starboard forward cockpit beside the companionway hatch. Make sure the hole you drill is small enough and in the correct location to be replaced by a compass for the next owner.

3) Raymarine EV-100 for hydraulic with the p70r head. Put the p70r inside the cabin so you can "power steer" with the dial. Put the chartplotter inside the cabin as well.

4) BWY full enclosure, cockpit cushions.

5) Snap-in canvas panel to close the engine well to cockpit throughway.

Done!