Please skool me on trim tabs!

[Toki]

I'm still figuring out my R27 classic. I'm a blowboater, and the idea of speeds above 8 kn and "getting on plane" are still alien to me. I've been reading through several posts here on trim tabs and also chatting with a couple others on the subject. I'm a little confused and am hoping to receive some guidance.

My understanding is a primary purpose of trim tabs is to get the boat on plane. Without the tabs, as speed increases the bow goes up and the stern carves a trench in the water, trim tabs enable you to quickly bring the bow down and plane level. So far so good???

OK, so now I'm cruising at 14 kn, boat is level, and planing (as much as an R27 with inboard can plane), but my tabs are full down. Isn't that inefficient? Aren't I burning diesel to churn water at that point?

I think I've read that once the boat is on plane and level, I should be able to retract the tabs and it stays level. Does that sound right? Doesn't work that way with my R27. I retract the tabs and the bow goes back up (not a lot, but up). Is this right?

I also understand using the tabs to level the boat out side to side if it's unevenly loaded, I have no confusion here, works well. I also understand that outboard boats involve a different equation as motor trim and trim tabs can be worked in concert, whereas I'm trim tabs only.

So .... Educate me!

Thanks

 

[asm777]

Check out this post on trim tab drop fin modification to improve trim tab performance

My understanding is that the trim tabs are to "adjust the attitude of the boat in the water" vs just to get the boat on plane.
I posted in the above thread this link that I found helpful in understanding the role of trim tabs:
https://www.sportfishingmag.com/boats/b ... -attitude/

Prior to making the drop fin modifications as shared by Brian (BB Marine) in the link above, struggled to stay on plane with a fully loaded boat even with tabs all the way down (If you see in my post in the previous thread, my use adds a lot of weight to the boat!). After the modifications, I can now "over-trim" and have to back off when I see that the bow is getting "too low" and it is affecting performance.

I typically set the tabs when heading is set and may have to adjust as we make course changes due to how the water/wind around the boat are affecting the boat's attitude. Also, if you have a lot of passengers moving around, it could affect balance and require adjustments.

Hope that helps some!

 

[Cutwater28GG]

(im not an expert and still learning) but my experience suggests with the inboard on the cut28 I dont trim to get on a plane. I know the boat is going to pop up onto the plane around 14-16 knots with enough RPM. the issue is managing boat attitude when underway when on plane

1. too trimmed down and the bow loves to steer off in random directions when it hits a wave: this is hard work on me and the autopilot
2. trimmed too high and the boat especially at even higher speeds can get pretty squirrely and feels like it loses contact with the water
3. i mostly trim left to right to handle current, wind, list, and people movement.

 

[Karll]

Trim tabs have several purposes but when the trim tabs are down they lift the stern to help with hull resistance. As you learn to use the tabs they help balance a boat depending on waves and (especially a light boat) where movement by passengers can tip a boat one way or another. It is easy to over compensate with a light boat so I would say once you tap the tab(s) wait a second to allow the boat to compensate to the change.

 

[vertigo]

I'm still figuring out my R27 classic. I'm a blowboater, and the idea of speeds above 8 kn and "getting on plane" are still alien to me. I've been reading through several posts here on trim tabs and also chatting with a couple others on the subject. I'm a little confused and am hoping to receive some guidance.

My understanding is a primary purpose of trim tabs is to get the boat on plane. Without the tabs, as speed increases the bow goes up and the stern carves a trench in the water, trim tabs enable you to quickly bring the bow down and plane level. So far so good???

OK, so now I'm cruising at 14 kn, boat is level, and planing (as much as an R27 with inboard can plane), but my tabs are full down. Isn't that inefficient? Aren't I burning diesel to churn water at that point?

I think I've read that once the boat is on plane and level, I should be able to retract the tabs and it stays level. Does that sound right? Doesn't work that way with my R27. I retract the tabs and the bow goes back up (not a lot, but up). Is this right?

I also understand using the tabs to level the boat out side to side if it's unevenly loaded, I have no confusion here, works well. I also understand that outboard boats involve a different equation as motor trim and trim tabs can be worked in concert, whereas I'm trim tabs only.

So .... Educate me!

Thanks

I'm not sure what a "blowboater" is, but I have the nagging feeling that too am one, so I'm fascinated to learn the answers. For me, I'm especially wondering at what hull speed or RPM an R29 Classic should be popping up on a plane.

 

[rpmerrill]

Also a former "blowboater". When sailing, as you know, you are always adjusting your sail trim to adjust to the wind and the sea condition. Always tweaking, right?
With your R-27, you can pour on the "gas" and let her run. Let's say you have a favorite speed, noise level, rpm or whatever. Getting up on plane is not all that big a deal. However, your trim tabs are the one thing you can still tweak. They don't do much until you get up to about 2500 rpm.

First off, they are helpful getting the bow down for better visibility of the water out ahead. ( I don't know if you have crab pots out west.). Second, as you trim the bow down you can feel and see on your GPS the improvement in velocity. If the sea conditions are right, that is what you are looking for. Watch your mpg on your GPS display. A trim adjustment can get you as much as 0.5 mph improvement and maybe even 0.2 mpg improvement. Not a great big deal, but as a sailboater, I know that gets your attention. Once you get into a trimmed state that you like , you'll know it and feel it. A one or two second, up or down tweak will show up on your GPS. Just do the tweak and wait 10 or 15 seconds to see the results. You'll see that too much trim will slow you down.

I mentioned the sea state. As you run you can notice out your side window that the bow wave/spray location will move forward or aft as you trim. If there is a little chop and a sidewind you can get spray that will blow up into your side windows. Adjusting the bow up will move that bow wave, and the spray farther aft. Also as mentioned above certain amounts of chop or swell will bounce your bow up and down. Trim can also do a lot to avoid that bounce.

In summary, be the sailor, enjoy the tweak !

One more tip. When you get back to the dock, retract your tabs all the way. This keeps the actuator shafts and seals in good clean condition. Put it on your checklist.

 

[Toki]

Thank you all for the great advice on trim tabs. Especially you rpmerril. Putting this in terms that even a sailor can understand really helps. I like your analogy to tweaking sails (yes, I'm very much a "tweaker"), and adjusting trim tabs to move that bow wave/spray back is brilliant, I never thought of that.

Thanks again everybody, I'm looking forward to experimenting with the tabs this spring!

 

[Toki]

OK, next round of trim tab questions. I was at the boat today doing some chores and checking out trim tab operation. Questions, again on my 2016 R27 Classic:

1. The tabs seem to only deploy about 5 to 10 degrees when full down, pretty much level when full up. Is this right? Should the deploy further than that?

2. When I deploy the tabs down, the pumps keep going indefinitely, even after the tabs are full down. When I deploy the tabs back up, the pumps stop when they're full up. Does that sound right?

Thanks all

 

[rpmerrill]

No expert here, but no, I don't think that's right.
When extending the tabs down you are taking fluid from a reservoir and pumping it into the tab actuators.
You seem to be getting a short stroke. I'm thinking that you are short of fluid, and the pump is running dry.

 

[FWTMD]

I am not YET an owner, but have seen where its important to fully retract the tabs when lifting the engine hatch. The tabs and hatch hydraulics use the same fluid supply, and the hatch won't fully open when fluid is directed to the tabs.

So it seems logical that if you were doing chores and generally messing around on the boat, you may have had the hatch open, leaving too little to fully activate the tabs?

Guessing.

 

[BB marine]

Full ram travel is 2.5 ". The reservoir fluid level should be checked with the rams fully retracted. There is a line on the reservoir tank to use as a gauge for filling or checking level. If the level is low there may not be enough fluid to extend the rams for full travel. The pump should not shut off automatically when full travel is reached. The pump will sound different at full extension because it is (dead headed) and running with a high load. When retracting the rams the pump pulls the fluid out of the rams back into the reservoir. Again the pump will not shut off automatically when the rams are fully retracted. The pump will have a different sound higher pitch with no load, no fluid to pump, causing pump cavitation. Running the pump for short periods after full travel is achieved or it is fully retracted will not hurt the pump or motor. Holding the trim tab switches down in either direction for long periods of time will cause the motor to get hot and the motor may stop running because of a blown fuse or an internal bi-metal breaker that protects the motor. If a fuse blew it would need to be replaced, If the bi-metal breaker opened it takes a few minutes for the motor to cool and the bi-metal breaker closes and the motor will function again.

I would suspect from your description of operation your fluid level may be low if the travel is less than 2.5"

 

[Toki]

Thanks for the advice all!

Brian, based on your description I think maybe my tabs are working as they should. Here are pics of one of the tabs full up and full down, looks like that may be about 2.5" ram travel.

 

[Dcsqatar]

Regarding general performance impacts of trim tabs, I believe the impact of tabs is influenced strongly by hull design. Prior to purchasing my R29S last year, I had been boating with a 24 foot bay boat with a 275 HP Yamaha. It had a shallow V planing hull, and the trim tabs had significant impact on not only boat trim but boat performance once on plane. I never did any careful testing and data gathering, but I can recall that optimizing trim tab position could add 5% speed at same rpm. Of course outboard engine trim optimization had even more impact.

With my R29, I noticed that the trim tabs would influence side-to-side list and bow-to-stern trim, but I was less certain of impact on performance. I therefore ran some tests which I have summarized in a table included in my photos. To gather data, I installed an inclinometer. My data showed little boat trim impact with deployment at 64% max rpm (or about 50% engine load) but significant negative impact onhull speed and fuel economy. At 83% max rpm (or 75% engine load) trim tabs were effective in reducing bow angle from 7 to 4 degrees with a slight decrease in hull speed (3%) and about a 5% improvement in fuel economy. My conclusion from this testing on the R29 mostly-displacement hull, is to not deploy any trim tab below 9-10 knots or so (unless balancing a list), and above that deploy to manage bow angle as needed.

 

[BB marine]

Brian, based on your description I think maybe my tabs are working as they should. Here are pics of one of the tabs full up and full down, looks like that may be about 2.5" ram travel.

Based on the pictures it looks like full travel. I would still confirm fluid level just to be sure.

My conclusion from this testing on the R29 mostly-displacement hull, is to not deploy any trim tab below 9-10 knots or so (unless balancing a list), and above that deploy to manage bow angle as needed.

.

Your Data seems very accurate for 29' water length. With 26' water line length the speed goes down lower to 7kts to 8kts. Anything above that requires tabs. Actually the C26 anything between 8.5 kts and 11 kts is what I call the dead zone use a lot of fuel and go no where. With or without trim tabs. I also agree Mostly displacement or Semi- displacement at best. Many use the term Plane loosely.

 

[Joan and Jim]

For safety, I have been told that, when in a following sea, the trim tabs should be retracted in order to keep the bow up. Otherwise a following sea may drive the bow down possibly causing the boat to broach.