quiet, smooth riding, good gas mileage

B

BaseCampAnne

New member
Perhaps this question arises from traveling to Gatherings that require quite a bit of travel to arrive:-) What is optimum speed for the 22' cruiser for quietness, smooth riding and best mpg? I am wondering what is the best way to experience all of the above? I heard from someone that getting up on a plane definitely affects (helps) mileage, but am a bit confused since the speed also affects mpg.

Another question: I imagine there are quite a few tricks and perhaps better boats, but at a steeper price...is there another boat that manages these 3 goals better than the 22' cruiser?

Anne
 
Anne, the issue is with resistance while in the water. Below planing speed, it takes a lot to push the hull through the water, once you come up on plane, the hull rests on top of the water and you'll note that once you reach that point, a little throttle results in a proportionately greater speed than off plane. Probably the most efficient speed is around 4-5 knots AFTER you begin to plane but it all depends on the boat, the cleanliness of the bottom, the load and all that stuff.

Experiment around, you'll find the "sweet spot".

Charlie
 
Charlie's (yuck, ptooie) right, Annie. I prefer using engine rpm vs speed and the sweet spot on the Jenny B is around 3500 rpm but I can vary around that +/- 500 rpm without much difference in mpg. I tune speed by local conditions but usually hang between 12 and 17 knots. Faster if I'm alone, slower if the bride is "resting."

So when are ya gonna visit your son again? Bay tours are cheap....

Don
 
Sneaks":2yuqelrs said:
Charlie's (yuck, ptooie) right, Annie. I prefer using engine rpm vs speed and the sweet spot on the Jenny B is around 3500 rpm but I can vary around that +/- 500 rpm without much difference in mpg. I tune speed by local conditions but usually hang between 12 and 17 knots. Faster if I'm alone, slower if the bride is "resting."

Don
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And a Yuck, Ptooie to you too! Let me see if you can have one of those undersea boats of yours get on plane.... :shock: Or even if I can get one of my targets to do it! :lol:

Charlie
 
Captains Cat":3hbliwl8 said:
And a Yuck, Ptooie to you too! Let me see if you can have one of those undersea boats of yours get on plane.... :shock: Or even if I can get one of my targets to do it! :lol:

Charlie
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LOL. Charlie, pre space era I used to say "What goes up must come down, but what goes down doesn't necessarily have to come up." (sigh) Nevertheless, you're still a good guy in my book, in spite of what Dusty told me.

You'd like Anne, btw. I think she'd be a fun Brat at any gathering.

Don
 
Well just to play devil's advocate, while I was slogging through steep wind-against-current 2-footers today, with the starboard wiper on constantly due to the splash, I watched some sailboats with envy. Deep, heavy, displacement hulls go pretty much the same speed I was able to maintain in those conditions.

Of course, they go that same speed when the water's glass-smooth, too. Oh, and they're more expensive. And longer and heavier.

But still, Anne, it COULD be that if you don't mind 7 or 8 knots maximum, a sailboat might make more sense. Of course, with that deep keel, you would find your cruising limited in other ways, too.

Ah, boats...They all involve compromises of one kind or another. The fact is that you CAN run your C-Dory at displacement speed (6 knots or so?), and it'll run relatively quiet, relatively smooth, and actually with really good fuel economy, if my fuel flow gauge is to be trusted (I'm not sure it is, though!).
 
Anne
I have to agree with Sneaks also. With my 22 My "sweet spot" is usualy somewhere between 3500 and 4200 rpms. Most of the time at the low end of the numbers. Was great meeting you at FH. Wish we could have visited more.

Chuck
Bootleg Hooch
 
RPM may be a bit missleading, since various boats are proped and engined differently...but there are few boats that size which get any better fuel economy, once the boat is "in the groove". After having gone from the 22 to the 25, and then adding the Permatrim, I feel that trim tabs and Permatrims will also improve the ride of the 22. One cannot set trim and speed and leave it there. I just ran about 45 miles, and speed varied from 7 knots up to 21 knots (trying to see what I could do with WOT on the 25). The amount of trim tab, engine trim bow attitude were diffent for each different sea condition. When it was really rough I was down in the 7 to 8 knot range, but in only a few minutes I was back up to 10 to 12 knots.

Having a fuel flow meter will give you a measure of effeciency at each speed.
 
A fuel flow meter sounds like it could help. I turn around and look but that is a wild guess, I know.

I also notice many boats have a guide that shows the "balance" of the perma trims. I am not sure what the real name is but as I have been experimenting I feel the boat flying way off to the right or the left and can be very lopsided! Almost scary lopsided. I am going to read up on the forum on perma trims to try to learn how to keep from the extremes! I know trying to adjust the two sides at the same time can be eventful!

Anne
 
Anne,

You may be confusing Permatrims with trim tabs. Permatrims are plates attached to the engines and are controlled by raising or lowering the engines. Trim tabs are plates attached to the transom of the boat and are controlled with rocker switches usually located somewhere around the instrument panel/steering wheel. Lowering a single trim tab a lot can indeed result in the boat veering and tilting (listing) in that direction as well. That can be unsettling! Trim tabs are used to lower or raise the bow of the boat and to control the side-to-side tilt of the boat. For example, if you are increasing the throttle and want to get the bow of the boat down so it will plane in a more level attitude you would gradually lower both trim tabs until the boat reaches your desired attitude. If you see that the boat is running with a side-to-side tilt and is not level you would lower or raise a trim tab to correct that and get the boat level. Note that the tabs will not always be lowered/raised an equal amount because of weight distribution on your boat. It is a matter of playing with the tabs in small amounts to get a feel for how they affect your boat. If, like me, you do not have trim tab position indicators, you learn to control them by eye and timing. On my boat it takes about 8 seconds for a tab to go from full up to full down so as I am raising or lowering them I count off the seconds to get an idea where they are within their range of travel. If you watch the horizon against your bow rails/line as you are moving one tab you will see how moving that tab "tilts" the boat to get to an even keel or to correct for weight imbalances. Trim tabs are for use when you are on or getting to plane. They have no real effect at slow speeds (5-7KTS), they just create drag and hurt gas mileage. It is important to remember to raise them up completely when you are preparing the boat to be put on the trailer and in following seas. Having them down in following seas can make your boat more likely to take water over the transom and is unsafe. It would perhaps be helpful for you to go out in calm waters and just play with them. Once you figure them out they are very helpful and your corrections become almost automatic.
 
C-cakes, a good post overall. I would add that even with trim tabs the tilt of the outboard remains an important factor. If for instance you do not have the outboard all the way down and forward but use the trim tabs more than 1/3 of the way then you will be less efficient.

The Capital Sea runs best wide open though. We always look the other way when refueling.
 
Hi Folks,
I'm sorry to post against what a few have said, but I disagree about fuel economy being better above planing speed. The subject has come up before in another forum (or 2), and somebody posted his gage readings within the past week or 2 I think, but I can't find that right now. But, take a look at this forum page http://www.c-brats.com/viewtopic.php?t=7603 to see some fairly hard info, incl. a chart which was given to me by our dealer showing rpm, speed, fuel flow and MPG for a C-D 25 with a Honda 150 (It think).
It sounds nice to say that you're pushing the hull thru the water when not planing, and skimming over it when on plane. But it takes a lot of power to lift the hull's weight up onto the water and keep it there. We sailed for 10 yrs or so, and hull speed is a known figure that depends upon hull's waterline length (almost exclusively), and is the speed which a displacement type hull of a particular length can be pushed thru the water before the power required becomes very high and it may try to rise and plane.
For example, a displacement hull with a water line length of about 25 ft (C-Dories are "semi-displacement" I think) has a hull speed of about 6 kts. To go something like 8 kts would require nearly twice the power. It's a square relationship, to double the speed you must quadruple the power. (again, this is for a displacement hull.) Our C-D's aren't really planing like a bass boat or hydroplane is, they're semi-displacement, and we use the trim tabs or motor angle & Permatrims to lift up the stern to make it seem to be fully planing. But we're dragging the tabs thru the water to lift the stern.
From what I've seen recently here with our boats, previously with others, and recently in my search for the same answer on larger semi-displacement boats, it seems to always come back that somewhat below planing speed is the most economical, fuel economy-wise.
We bought our 25 last Summer after sailing in a 27 ft sloop for 8-9 yrs (12 HP to go at 5-1/2 kts, under power). We have enjoyed being able to get places faster (e.g. Oriental for lunch) with the planing boat, but have decided we'd like a little more creature comforts so have listed the C-D 25 for sale within the last week. We're looking for something a little larger, with an inboard, and have been looking closely at the Mainship 30 Pilots. Twice the weight, twice the HP, but can go at just below hull speed at about the same fuel consumption, and not much worse than the 25 at comparable planing speeds.
Lots of words, I haven't dug for formulas to back it all up with, but I'll stand by the general thoughts.
 
BaseCampAnne":3557j0gd said:
A fuel flow meter sounds like it could help. I turn around and look but that is a wild guess, I know.

I also notice many boats have a guide that shows the "balance" of the perma trims. I am not sure what the real name is but as I have been experimenting I feel the boat flying way off to the right or the left and can be very lopsided! Almost scary lopsided. I am going to read up on the forum on perma trims to try to learn how to keep from the extremes! I know trying to adjust the two sides at the same time can be eventful!

Anne
Click to expand...

A fuel flow meter that can use GPS data will give you mpg, which is what
you really want. Surprisingly, my mpg does not vary much with speed with
rpms running anywhere from 3800-4600 or so. That's with a Honda 90,
5400 max rpm.

I also installed a little gauge that helps you know when the boat is
running absolutely level (side-to-side). Leveling the boat by even a
degree or two helps with fuel economy and you get a better ride.

Mike
 
Al,

My CD-22 certainly gets better milage off plane. Something like
8 mpg off plane, and 3.6-4.1 mpg planing. At really slow speeds -
less than .5 gph, the flow meter does not register. I think that's about
4mph...? I forget exactly. At those speeds, current is a major factor
that you have to take into account as well.

Mike
 
Time is the major factor that I have to consider. 10 knots is fine if you are retired, but I have only so much time to get some place.( and going slow drives me crazy) so its a balance between speed, mileage , comfort, room etc. right now the 22 dory is good for me but i will be moving up to something bigger and faster or at leas as fast but better in the chop. And yes it will cost me three times as much. From some its just bigger and slower is ok. for some its speed and low mileage is ok. You just have to figure out your mission and than find the best good looking boat to fill that mission. right know we are looking at the RF-25 , the ranger tug and the Seasport pilot house 26. they all fill my mission its just that one is better then the other at a differnet part of the mission. I have to weight which part of the mission is most important.
 
Thomas, so will you be selling the Susan E?? With the art work and that fish box and overall condition, as auction may be in order.
Still, I hope you will not.
A sound boat with all the toys......$40K - $60K
The Cbrat family........................ Priceless


And, in regard to your post, I would agree. It is not a question of at what speed you get the best gas milage, but a question of getting the best gas milage at the speed you want to travel. The 22 gets me there at greater economy at 20mph and also at 30+ and though it may beat all others below plaining speed, that is too slow in good water.
 
starcrafttom":2y60yu67 said:
.( and going slow drives me crazy) so its a balance between speed, mileage , comfort, room etc. right now the 22 dory is good for me but i will be moving up to something bigger and faster or at leas as fast but better in the chop. And yes it will cost me three times as much. You just have to figure out your mission and than find the best good looking boat to fill that mission. right know we are looking at the RF-25 , the ranger tug and the Seasport pilot house 26. they all fill my mission its just that one is better then the other at a differnet part of the mission. I have to weight which part of the mission is most important.
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Mr Elliott,
I know it's not my business, money or decision but I think you left out the best candidate. The TC255 is priced lower than what you listed, much faster than what you listed, more roomy than what you have listed, rides just as well or better than what you listed and you would still be a bonafide c-brat :smiled Gotta keep the cool factor!
I think there is still a great deal on one in Palatka FL at Big boy toys. A good ways away from you but you could do the reverse of what a lot of brats have done in this part of the country. Enjoy the waters here during your harsh winter time and then drag it home. :thup
 
Jeff I have looked fished out of and drove the cat and really love it, but with twin motors that gas gage goes really fast. What is your fuel burn at 24 mph? 10-14 gph??

AS far as selling the susan e , it will happen some day but not this year unless buisness really takes off, want to buy a house?? We will of course put new art work on what ever boat we get in the future and we will show up at brat events to see the gang, cant stop me from that. and who knows maybe the new owners will finally build the boat that they should re-interduce, the 27 pilot house that the guy in alaska has( boat name AVIQ). That boat with the right engine is the one I really want.
 
With time as important figured in, push it just past a plane.

When time is not important, take plenty and poke along.

Learn to use your ears as an rpm gauge and they can tell you things electronics won't.


C.W.
 
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