Fuel burn rate influenced by trim tab positioning

[baz]

Has anyone good intuitive advice for operating the trim tabs to minimize the fuel burn rate ?

One of the bits of info Andrew gave me during our sea trial was that trim tabs were useful to control fuel burn. I have used the tabs for this purpose and sometimes the fuel burn rate changes either up or down. Sometimes the rate change is almost unnoticeable and can be up or down at times. It seems that our R-25 has to be above 10 Kts before any noticeable fuel burn rate change can be obtained.

Maybe more knowledgeable people can chip in here and provide good advice and/or techniques on how to control the fuel burn rate using the trim tabs and what affect should be expected at various speeds.

Thanks... 🙂

 

[Bruce Moore]

Barry,

I've found, with many things, the hardest lesson to learn is how easy it is. Cruise around in your boat, vary the trim, and watch your burn - GPH or MPG. Do it at various speeds. You'll get a feel for how trim affects burn. Basically, you don't want to be cruising up hill, or digging your nose in. Find the place where you move less water out of the way. Play with the tabs and track the feedback. You'll see it in the metrics, see it in your boat's attitude, and you'll feel it. Once you feel it, you won't have to track it.

And, you'll find there are times when trimming for sea conditions trumps trimming for fuel efficiency.

 

[Longbranch Louie]

As a new 25 owner Im also trying to get the feel of using trim tabs. The tab effect seems less on the tug compared to a higher speed cruiser. One thing Im learning is 10 knots is not always 10 knots. Here in the south sound we can get pushed an extra 3 or 4 knots running with the tide and lose knots going against it. Your doing 10 knots but the amount of fuel burn and rpm to reach 10 knots varies alot. With a 3 knot tide behind you gps speed might read 10 knots but would the tugs actual speed be enough to get any affect from using tabs??
These added variables along with wind and chop have given me fits on trying to get the feel for best tab placement. Someone told me the spray should be just below the pilot window when its right??? My wife is getting tired of my head being out the window. I agree its more feel than gauges when its right.

 

[Levitation]

1. Place cup of coffee/tea in the holder next to you.
2. Motor out into open water
3.look around before opening throttle
4. Advance throttle to RPM you have chosen in advance / 2500-3000 is a good starting point
5. Watch bow rise up to an impressive degree
6. After everything is stable use trim to lower nose a small amount
7. Sip tea and let speed stabilize
8. Does steering seem a little loosey-goosey? If so blip nose down a hair. Wait. Repeat as necessary
9. Give up and leave the trim where it was after your 27th adjustment
10. Tap fingers on the helm in time to the music. Sip tea. Ask the Admiral where you should do dinner

The whole point is that the adjustment is done by feel. If it feels good then it is good. Forget the speedo (except under dead calm conditions or a major attack of OCD)
Forget "improving" the fuel burn by constantly playing with the trim - at most you are going to change it by a few tenths of a gallon per hour.
Don't over think it - Be happy

 

[baz]

Thanks guys... 🙂

You've confirmed that I've not been out of my mind posting this topic. It seems there will be times when fuel burn rate can be noticeably reduced and then there will be times when it cannot no matter how much coffee or tea one drinks.

Somehow I was wondering if I had missed some important details about operating the trim tabs when on the sea trial with Andrew, just like I had using them to control the boat's attitude that I posted in another topic.

It's kind of a feeling the boat is running/gliding/skimming and is simply at ease with itself... simply don't 'over think' and be happy the boat is behaving nicely.

I must admit, I haven't tried the head hanging out the window trick though... my 1st mate seeing me do that would cause her to think she's said something awful to me, or worse still, my 18 month old Wire Hair Fox Terrier Jake would jump/leap onto my lap and demand to be included in the fun and games. :lol:

When I started to read Levitation's post I jumped to the conclusion immediately hoping that by simply observing a cup of coffee/tea placed in the holder I could use that to gauge when fuel burn rate was optimum, but after reading on found that that was simply a distraction from the task at hand.... and one should simply give up after the 27th trim tab adjustment... 😉

I've never attempted to obtain less fuel burn rate when in strong current, big waves, choppy waves, strong winds, etc and pay more attention to running the boat as smoothly as is possible by varying the boat's speed and direction with the trim tabs in the fully up position and leaving them alone.

It's only when the seas are relatively calm and there's no noticeable current pushing me around that I 'play' with the tabs to see if I can thwart mother nature some.

At the Fishermans Terminal meeting I will take the boat out onto Lake Washington where it could be calm and with no to little wind and play and drink plenty of tea just to convince myself the trim tabs can in fact affect fuel burn noticeably or not. 😉

I feel much better now having read your posts. Thanks...

 

[Stella Maris]

I applaud Denny for his great response and reasoning! Some people have the tendency to over think this entire experience. Boating should be fun, not a mathematical equation.

Great job Denny!

 

[baz]

I applaud Denny for his great response and reasoning! Some people have the tendency to over think this entire experience. Boating should be fun, not a mathematical equation.

Great job Denny!

Oh David... you miss my point here entirely... I do believe Denny was seriously trying to answer my OP... and he did a good job as did Bruce and Longbranch Louie.

Building one's knowledge base enhances the fun factor, otherwise the 'fun factor' could lead to dire consequences. :roll:

 

[Stella Maris]

Barry, you missed my point here. I simply pointed out that Denny hit the nail on the head that some people tend to over analyze and over think these situations but, if the shoe fits....

 

[baz]

David... It's too easy these days to misunderstand.... so, sorry if I misunderstood you. Take care and have fun this weekend. Read your other post just now and this weekend will be glorious in the local PNW Puget Sound area. Can I track you using the AIS website ?

 

[Stella Maris]

Barry,
We are only equipped with receive only AIS. We are currently passing Edmonds bound for Hat Island outside of Everett. We will meet John and Laurie there and spend the night at the marina as their guests.

David

 

[baz]

1st Mate has looked out and seen the weather... :roll: so, we shall also be out of Edmonds marina and onto the Sound shortly... 😀

I was wondering where those awful coastal hill slides are on Whidbey Island... suspect they are on the West side though...

Yea... I searched for Destiny and came up with several but they were not anywhere where you indicated you were at. 🙁 Where did you exactly anchor in Port Madison ? Near Treasure Island maybe ?