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OK I am still confused on the prop/engine
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thataway



Joined: 02 Nov 2003
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PostPosted: Sun Jul 06, 2014 10:58 pm    Post subject: Reply with quote

What sort of fuel flow meters are you all using to measure efficiency? When I note efficiency, this implies better mileage. (As measured with fuel flow meters). Not sure how to measure efficiency unless you are able to document fuel usage at a specific speed--not as per a tank full, which does not measure at specific speeds.
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Thataway
Thataway (Ex Seaweed) 2007 25 C Dory May 2018 to Oct. 2021
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colbysmith



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PostPosted: Sun Jul 06, 2014 11:23 pm    Post subject: Reply with quote

I actually have a fuel flow meter on my single, as part of the Navman Unit. However, it's almost useless as the 115 4-stroke EFI must work in a way that cycles fuel into it's own system, as my meter will fluctuate at stable RPMs... But I think over time, just using gallons per hour gives one a pretty good idea how they are doing. And then maybe tracking miles per hour... Smile
Colby
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Sunbeam



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PostPosted: Sun Jul 06, 2014 11:35 pm    Post subject: Reply with quote

thataway wrote:
What sort of fuel flow meters are you all using to measure efficiency? When I note efficiency, this implies better mileage. (As measured with fuel flow meters). Not sure how to measure efficiency unless you are able to document fuel usage at a specific speed--not as per a tank full, which does not measure at specific speeds.


Well maybe I'm all washed up as I am just going by sound of the boat, feel of the boat, and speed/RPM. Here is what occurs:

1) I get up on plane and am cruising along. The bow is not down; in fact it is "up" unless or until I use the trim tabs to trim it down (which I do in chop).

2) The engine is trimmed all the way down/in.

3) I am going at X speed (let's just say 25mph for the sake of example) and X RPM.

4) I decide to try trimming the engine up/out, as I know I'm "supposed" to be able to, and I want to see what happens.

5) What happens is that the boat/engine get noisier, and my speed goes down. I have not touched the throttle.

I gather from this (increased "fussier water" sounds from the engine, reduced speed) that it's less efficient. I don't have a fuel flow meter and actually the fuel consumption isn't my major focus (although of course it's nice to reduce it). I was just speaking of efficiency/pleasantness/speed of the boat running. Essentially, the boat runs "happier" with the motor trimmed all the way down/in, and if I trim up/out at at all, it gets less happy (noisier, slower, etc.).
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thataway



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PostPosted: Sun Jul 06, 2014 11:52 pm    Post subject: Reply with quote

Glad you have a "Happy" boat Sunbeam…!

Is your best WOT speed with engine trimmed down all of the way ?

Colby, with engines which recycle fuel you have to use a Flow Scan, which will measure fuel in and fuel returned (as also in diesels). With an E Tec, you should be able to get fuel burn off the NMEA 2000 computer output.
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Sea Wolf



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PostPosted: Mon Jul 07, 2014 12:01 am    Post subject: Reply with quote

Sunbeam wrote:
thataway wrote:
What sort of fuel flow meters are you all using to measure efficiency? When I note efficiency, this implies better mileage. (As measured with fuel flow meters). Not sure how to measure efficiency unless you are able to document fuel usage at a specific speed--not as per a tank full, which does not measure at specific speeds.


Well maybe I'm all washed up as I am just going by sound of the boat, feel of the boat, and speed/RPM. Here is what occurs:

1) I get up on plane and am cruising along. The bow is not down; in fact it is "up" unless or until I use the trim tabs to trim it down (which I do in chop).

2) The engine is trimmed all the way down/in.

3) I am going at X speed (let's just say 25mph for the sake of example) and X RPM.

4) I decide to try trimming the engine up/out, as I know I'm "supposed" to be able to, and I want to see what happens.

5) What happens is that the boat/engine get noisier, and my speed goes down. I have not touched the throttle.

I gather from this (increased "fussier water" sounds from the engine, reduced speed) that it's less efficient. I don't have a fuel flow meter and actually the fuel consumption isn't my major focus (although of course it's nice to reduce it). I was just speaking of efficiency/pleasantness/speed of the boat running. Essentially, the boat runs "happier" with the motor trimmed all the way down/in, and if I trim up/out at at all, it gets less happy (noisier, slower, etc.).


Sounds like you're ventilating!

With the engine trimmed down (forward), the boat thrust lifts the stern, but also keeps the anti-ventilation plate under the water flow off the stern of the hull.

With the motor tilted up (backward), the bow rises excessively, the water flows downward as it leaves the back of the stern from the pitched-up hull, and the anti-ventilation plate catches some air at the front, spins faster and more noisily (but not enough to raise the rpm over the redline excessively), you lose some of the thrust with the air mixed in, and the boat slows down.

I'd think this could be because the engine is mounted too high, with the anti-ventilation plate's high position being the real culprit.

This may or may not be right, but it's what I'd guess from your description.

Joe. Teeth Thumbs Up

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Sunbeam



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PostPosted: Mon Jul 07, 2014 12:12 am    Post subject: Reply with quote

thataway wrote:
Glad you have a "Happy" boat Sunbeam…!

Is your best WOT speed with engine trimmed down all of the way ?


Yes it is. If I trim the engine up at all from "full down," my WOT speed is reduced.
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thataway



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PostPosted: Mon Jul 07, 2014 12:15 am    Post subject: Reply with quote

Then I would suspect that there is an issue with the way the motor is mounted. My experience is that motor trimmed all of the way down is not going to get the highest RPM for WOT. (Specifically in two C Dory 22s and one C Dory 25--as well as a number of other small relatively fast boats). If your Permatrim is not running on the surface (which I believe you said it was not), then the motor is lower than ideal.
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Sunbeam



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PostPosted: Mon Jul 07, 2014 12:20 am    Post subject: Reply with quote

Sea Wolf wrote:


Sounds like you're ventilating!

I'd think this could be because the engine is mounted too high, with the anti-ventilation plate's high position being the real culprit.


Actually, I believe the engine is set a bit too low. I say this only because, in another discussion here, someone posted links to photos showing how the Permatrim/anti-ventilation plate is supposed to ride (nearly at the surface of the water that you can see). I happened to just have taken the same angle of photo of my engine when running along at speed. My plate is much lower than they show. Also, Roy of "Roy & Dixie" has the same engine as me, in the same position, and found the same thing. He raised his engine two holes and found it overall improved (not sure about how he trims the engine though).

Too bad I didn't check it out more before adding the Permatrim, just for data. I only ran it that way on the initial sea trial though.

But, I'll experiment - starting with moving the engine up a couple of holes like Roy did - and see what happens. It would be nice to be able to make some use of the trim feature on the engine. Seems like if it is there, I should be able to put it to some good use.
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T.R. Bauer



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PostPosted: Mon Jul 07, 2014 12:23 am    Post subject: Reply with quote

Since I have had twins (honda 45s) for around 2000 hours of usage, I can tell you I can travel with ease at 20-24 mph when loaded and turn around 4800-5000 rpms. My max rpm is really close to 6000 rpms and moves the boat a hair or two over 30 mph. Just a couple of days ago, the boat had 3 heavy adults and 2 kids on board and we came back with 200 pounds of halibut in the fish box I made for the splash well and still had no trouble going 23-25 mph on flat water. I could have even gone faster without trouble, but don't like going past 5000 rpms in general. Unless you are operating your boat at elevation or something, your performance numbers are way off as we are only talking about 10 hp (I think).
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Sea Wolf



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PostPosted: Mon Jul 07, 2014 12:25 am    Post subject: Reply with quote

Sunbeam-

Sounds good to me!

Give it a try!

Joe. Teeth Thumbs Up
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Sunbeam



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PostPosted: Mon Jul 07, 2014 12:27 am    Post subject: Reply with quote

thataway wrote:
Then I would suspect that there is an issue with the way the motor is mounted. ... If your Permatrim is not running on the surface (which I believe you said it was not), then the motor is lower than ideal.


That is the case, and I suspect the same as what you say (I think it may have been your link that had the photos of the correct height).

Interestingly, I have been looking at where the four transom holes are on a number of 22 Cruisers. They all seem to be in close to the same location - so perhaps there is some "usual" guideline for where to put them. However, the "hole heights" used on the engines vary. For example, mine is set in the second hole down from the top and there are four adjustment holes. So I could raise my engine two holes (and probably will).

Theoretically the holes in the transom could be slightly higher, but not very much because the washers/backing plate on the inside of the transom would come up over the top edge.
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Chester



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PostPosted: Mon Jul 07, 2014 4:21 am    Post subject: Reply with quote

13" pitch 3 blade props are common on 22's with twin Honda 40s for low altitude use. They let our 40s rev to 6,000 rpm which is ideal.
I tried raising my engines to get the anti ventilation plates out of the water while on plane but it really limited the amount of trim I could on the engines. Any small (very small) gains in speed weren't worth it.

Question. How much would the pitch need to be reduced when going to 4 blade props with an eye on trying to encourage stern lift? Or is this just foolishness with a 16 knot cruise speed?
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thataway



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PostPosted: Mon Jul 07, 2014 12:08 pm    Post subject: Reply with quote

Chester wrote:
13" pitch 3 blade props are common on 22's with twin Honda 40s for low altitude use. They let our 40s rev to 6,000 rpm which is ideal.
I tried raising my engines to get the anti ventilation plates out of the water while on plane but it really limited the amount of trim I could on the engines. Any small (very small) gains in speed weren't worth it.

Question. How much would the pitch need to be reduced when going to 4 blade props with an eye on trying to encourage stern lift? Or is this just foolishness with a 16 knot cruise speed?


You want the anti ventilation plate/foil, just on the surface of the water, not out of it--and a lot depends on the dynamics of the water flow off the transom.

One inch pitch reduction is suggested for a boat going from 3 to 4 blades.
However, There are some good 3 blade stern lifting props. If I was going to explore this, I would contact Ken at Prop Gods. Prop Gods has a forum, and it is good reading.

http://www.propgods.com/forum/



Often similar questions are asked at The Hull Truth, and Scream and Fly forums..

A comment from Ken on one of the forums: "Blade design and geometry plays a very large role in the way a prop carries the boat. Its not just the number of blades….
When we wrote the FAQ section, its basically just "general" answers for most conventional boats.
In reality, every setup is different, and the characteristics of certain props can vary depending on the setup and what your comparing it too."

Going to SS speciality props can be expensive, and there may not be a lot of change for a bunch of $$$. It sounds as if you are fairly well dialed in--especially in relation to what ranger is experiencing. Back to the axiom that pitch is not the entire issue. First the boat has to be right, then the motor position/trim has to be right, and finally the prop.
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Chester



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PostPosted: Mon Jul 07, 2014 1:59 pm    Post subject: Reply with quote

Thank's, Bob. I worded that poorly, should have said the motors were raised one hole to get the AV plates out from under water while on plane.
The AV plates are the same height as the hull bottom now (again) and removing the wedges haven't caused any issues so far.
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jerry97230



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PostPosted: Mon Jul 07, 2014 3:58 pm    Post subject: Reply with quote

I have gwin 40 Hondas. I recently bought two new props and had the old ones tuned up.
They are the same size and pitch, but the new ones are a bit slower than the old ones.
I have put the old ones back on and am saving the new for spares.
Jerry C Nile CD22
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