Trim tabs required?

[rbcoomer]

Can I solicit some views on trims tabs please?

I'm particularly interested in any impact on more efficient cruising in mid-range power (20-30kts) and best possible stability.

I am in the process of gutting and rebuilding an early style 21' Fletcher Arrowbolt - late 70's or early 80's style inboard with cuddy (not later Sports Cruiser type). I'm aiming to get her on the water by early/mid 2013. I have more than enough to be getting on with so not looking for work for the sake of it, but I want the job to be the best I can, so don't want too much retro-fitting.

Is fitting of trims tabs necessary/beneficial on a 21' boat of this style and if so, what would be a sensible product to look at for that won't burn a massive hole in my wallet or be overkill...?

Our 14' handles great, but is quite hard to 'balance' - requiring passengers to move around to avoid her heeling over. The Arrowbolt is obviously a little bigger, but we're more likely to have extra people too. I've also been told that these hulls can have a tendency to 'chine-walk' at high speeds (60kts+)? I'm not really looking to achieve that pace and envisage my setup will probably max-out at around 50-55kts anyway - more than enough for us & my experience level.

I'm perhaps 6 months away from this currently as I'm still replacing floor/stringers, but like to keep a longer-term view on what's needed to enable better planning and steer current decisions. I also find it useful to monitor the market for bargains on my wish-list before I need them! A good example of this is heating where I intend to install all the ducting etc under the floor, but not actually install the heating yet. The advantage here is that I can pick up a heater as and when a suitable bargain arises budget delaying the overall project. Should I just wait until I can sea-trial her and then review/retro-fit?

There is a degree of modernisation anyway in the rebuild and some 'practical' alterations for more all year UK boating. It's unlikely that the original balance will be maintained as there will inevitably be some extra weight here and there (if that's of significant importance) .

Once finished the boat will be be less speedboat and more of a compact coastal day cruiser. Albeit mostly open (with camper cover) and keeping her classic lines - also quick enough to run for refuge when needed! Whilst the Fletcher hulls have a good reputation for off-shore racing and thus capable of handling the seas, I'm looking for less speed and maximum stability. Ultimately I want to be able to cruise all around the South West (from various launch sites but mostly Torbay) with perhaps a 100 mile range that I can build towards steadily over a few seasons. She has the advantage of being small enough to trailer and sneak into all the best Westcountry inlets, rivers etc, but just about do-able for an occasional overnight/extended voyage...

Notable extra weight items will be anchor/anchor locker (not present currently, auxiliary outboard (somewhere in the 4 to 9 hp range?), extra batteries, heater (& small diesel tank), radar arch and electronics - none of which were previously fitted. If I can figure a means to fit, a chemical loo too!

Thanks in advance as always and apologies for the long waffling post!

 

[maverickofpoole]

I didn't read your entire post but can say when I owned a 6 metre sports fisher (Warrior 195 with 150 opti) I found hydraulic trim tabs a boon for the following reasons:

Weight distribution
Attitude ie more bow down/up
Beam on wind
and variants of the above.

They just make it so much easier to balance trim and get the most efficiency out of a boat, all with practice of course

Well worth fitting imho

Martin

 

[rbcoomer]

I didn't read your entire post but can say when I owned a 6 metre sports fisher (Warrior 195 with 150 opti) I found hydraulic trim tabs a boon for the following reasons:

Weight distribution
Attitude ie more bow down/up
Beam on wind
and variants of the above.

They just make it so much easier to balance trim and get the most efficiency out of a boat, all with practice of course

Well worth fitting imho

Martin

Thanks Martin - yes I did get a bit carried away! Realised after I hit submit - t'was almost a book!

Cheers for the feedback.

 

[markcw]

Hi rbcoomer
You think my thoughts, i to have recently been thinking of hydralic trim tabs on mine, but the cost is alot more than i thought, i have looked at the fixed postion ones, but realised this will only be used for getting the boat on the plan quicker which my 21 ft boat has no issue with haveing a v/p V6 inboard.

If i could get a second hand trim tabs i would take the plunge and try.

 

[rbcoomer]

Hi rbcoomer
You think my thoughts, i to have recently been thinking of hydralic trim tabs on mine, but the cost is alot more than i thought, i have looked at the fixed postion ones, but realised this will only be used for getting the boat on the plan quicker which my 21 ft boat has no issue with haveing a v/p V6 inboard.

If i could get a second hand trim tabs i would take the plunge and try.

Hi Mark,

I've been looking at Lectrotab - which would out around £650-£700 I think. I suspect it's more a 'nice to have' on a 21', but if as I suspect the benefits of better poise and control translates to better economy then they're probably worthwhile! I have 100L tank which isn't going to be cheap to fill and if I can improve economy by say 5% then worth considering... I'm thinking ahead largely because of wiring and dash layout etc - which could make a later fit messy. Plan B would be to do some 'bare hull' sea trails and put her through her paces before I do the interior fit-out etc. I'd agree that there's little point in manual - I think they need to be dynamic and controlled from the helm.

Hence the post to hopefully get an idea who's fitted what and how successful?

Regards,

Robin

 

[Scillyboy]

I've invested in a Bennett tabs (hydraulic) kit for a 20ft Hardy, which I'm about to fit when it's a bit dryer/warmer. Probably too late to be of much help, but I can report back on the ease of fitting and achieved improvements (hopefully, trimming, and better general stability at speed) once it's back in the water. It seems that basic kits can be had currently from £400-£500; more if you want position indicators.

 

[MapisM]

Our 14' handles great, but is quite hard to 'balance' - requiring passengers to move around to avoid her heeling over.

No experience on the Fletcher, but as a rule of thumb I'd expect a 21' boat to behave only marginally better.
You're still talking of a size where one passenger moving from port to stbd on the rear bench is more than enough to make the boat list, let alone cruising in some crosswind.
On top of that, on a 21' capable of 50+ kts, trim tabs indeed allow a better control of the boat.
You mentioned chine walk, that's something which typically can be cured by tabs, even if maybe at the expense of the last few knots.
Many 20-25' boats are much more stable and predictable at high speed with tabs, even when set neutral (=level with the hull).

 

[STEVEDUNSTABLE]

hi rbcoomer......i have eltrim,s on my S24...as the name says they are electric not hydraulic which would cut out lots of "plumbing"..they can also be used "individualy" for fine adjustment underway...it took me yonks to get the "knack" of how sensitive they are BUT, on a calm day, a small "tweek" on them can give me upto 1.5knts for no extra revs !!!!...and as you say, they really can help with "bodies" moving about..sorry i can help with any other makes of tabs...regards steve

 

[AndieMac]

I'd be tempted to get the boat completed first Robin, run it though it's paces, then make a decision. They are easy to retro-fit.

 

[BarryH]

I'd get it on the water first. When we had our Tremlett I looked at fitting tabs. The Tremlett leaned into the wind on the plane, only to stbd though. I looked around at various makes and was amazed at the costs. At the time it it just wasn't affordable.

In the end I shifted around the way the gear was stowed and fitted a set of Doel-Fins onto the Volvo drive. It made a big difference for not a lot of money.
I'd wait if it were me to see how all the extra gumph affects the boat. The Tremlett isn't too much different from the Fletcher in the stern sections of the hull.

 

[landlockedpirate]

I dont think trim tabs will be of much benefit on your boat, the Fletcher hulls tend to self level when you trim the leg out.

What engine have you got ? 55kts seems optimistic without serious power upgrades. I would thing 40-45kts more realistic and it wont chine walk at that speed unless the set up is seriously wrong.

FWIW I would wait and see before you blow a big hole in your budget for something that may not be needed.

 

[rbcoomer]

Thanks everyone - a fairly mixed verdict as expected but all useful.

I think I'm leaning towards a 'bare hull' shakedown (any excuse ) during the summer - before I do all the trim and interior fitting! I've not heard anything detrimental yet towards the electronic variants so I think that would be my choice and thus less of an issue to retro-fit. I wondered about electronics outside the boat in such a hostile environment, but encouraging to hear positive feedback - thanks.

Scillyboy - will look forward to hearing how it goes and what benefits/improvements result!

Landlockedpirate - 5L Penta (AQ231 I think, but no identification that I've yet found). Coupled to a Alpha 1 Gen 1 drive and a 19p prop. My maths are probably awry, but I calculated 56.7mph @ 5200 or 45.8mph @4200 (found conflicting info on max rpm for the 5.0's and if it does just happen to be a bigger lump...! ) I'm not really after speed and if she'll cruise comfortably in the 30-40kt range that'll be great!

Cheers,

Robin

 

[MapisM]

My maths are probably awry, but I calculated 56.7mph @ 5200 or 45.8mph @4200 (found conflicting info on max rpm for the 5.0's and if it does just happen to be a bigger lump...! )

Your math is correct, but from where did you get the 10% prop slip which you seem to have assumed in your calculation?
I'm not saying it's wrong, but that depends on many factors (prop/hull/drive/x dimension), and unless you have some reference with a similar boat, it's only possible to calculate it ex-post.
Anyway, re. the RPM, 4200 and 5200 are too low/high respectively, for the 5 liters block. I would aim at a 4600 WOT RPM, ideally.
Which still gives a respectable 50/51 mph, keeping your slip assumption.

 

[rbcoomer]

Your math is correct, but from where did you get the 10% prop slip which you seem to have assumed in your calculation?
I'm not saying it's wrong, but that depends on many factors (prop/hull/drive/x dimension), and unless you have some reference with a similar boat, it's only possible to calculate it ex-post.
Anyway, re. the RPM, 4200 and 5200 are too low/high respectively, for the 5 liters block. I would aim at a 4600 WOT RPM, ideally.
Which still gives a respectable 50/51 mph, keeping your slip assumption.

Thanks - I'd seen reference to 5600rpm somewhere, but the AQ231 manual I found online suggested 4600 max. I took off a bit for age and margin for error as I'd hate to blow it up!

The 10% was a non-scientific 'stab-in-the-dark' - I felt I needed to factor in something

 

[MapisM]

The 10% was a non-scientific 'stab-in-the-dark' - I felt I needed to factor in something

LOL, I should have guessed that.
That's actually a reasonable assumption, anyway.
The prop is the standard 3 blades alu, I suppose?
If so, you might wish to consider a s/s prop, if you'll need to tune the boat a bit. At that sort of speed, steel begins to make a difference vs. alu.

 

[rbcoomer]

LOL, I should have guessed that.
That's actually a reasonable assumption, anyway.
The prop is the standard 3 blades alu, I suppose?
If so, you might wish to consider a s/s prop, if you'll need to tune the boat a bit. At that sort of speed, steel begins to make a difference vs. alu.

Yes a cheap ali one. The original was a 17p ali, which I sent to Steel Developments as it was a bit tired with a small 'bite' missing. However it was too badly electrolysed and they said it couldn't be welded. The general consensus was that 17p was too 'sharp' a pitch anyway and that 21 or even 23 would be better. On the basis that I needed something, I opted for caution with the 19p - being in between. I'll stick with this until the boat is finished, fitted etc and I've done a few genuine trips in different conditions and then look to optimise with a stainless prop and keep the 19 as a spare. Thus I don't think the 50mph is so wide of the mark ultimately and the trim tabs might be relevant...

 

[MapisM]

Yep, I also think that trim tabs are more than just nice to have, at that sort of speed.
It's one of those things wihch you must try to appreciate.
Anyway, there's nothing wrong with the previous suggestions to try the boat first.
You'll always be able to fit them afterwards, though obviously you'll have to lift the boat.

Re. the prop, actually I was wondering if a 5.0 engine on a light 21' shouldn't be able to spin a bit longer prop.
Anyway, just start with what you've got and see the results.
With props, there are only 3 ways to find the optimal one: test, test and test.

 

[rbcoomer]

Hmm - test, test and test eh? I like the sound of that - best excuse yet for more hours on the water...

 

[Scillyboy]

I've made a note to post again when the tabs are up (or down ) and running....though from what I've read here, you will be operating some way beyond my capabilities - 25kts is all I can manage!

 

[sparticus71]

Can I solicit some views on trims tabs please?

I'm particularly interested in any impact on more efficient cruising in mid-range power (20-30kts) and best possible stability.

I am in the process of gutting and rebuilding an early style 21' Fletcher Arrowbolt - late 70's or early 80's style inboard with cuddy (not later Sports Cruiser type). I'm aiming to get her on the water by early/mid 2013. I have more than enough to be getting on with so not looking for work for the sake of it, but I want the job to be the best I can, so don't want too much retro-fitting.

Is fitting of trims tabs necessary/beneficial on a 21' boat of this style and if so, what would be a sensible product to look at for that won't burn a massive hole in my wallet or be overkill...?

Our 14' handles great, but is quite hard to 'balance' - requiring passengers to move around to avoid her heeling over. The Arrowbolt is obviously a little bigger, but we're more likely to have extra people too. I've also been told that these hulls can have a tendency to 'chine-walk' at high speeds (60kts+)? I'm not really looking to achieve that pace and envisage my setup will probably max-out at around 50-55kts anyway - more than enough for us & my experience level.

I'm perhaps 6 months away from this currently as I'm still replacing floor/stringers, but like to keep a longer-term view on what's needed to enable better planning and steer current decisions. I also find it useful to monitor the market for bargains on my wish-list before I need them! A good example of this is heating where I intend to install all the ducting etc under the floor, but not actually install the heating yet. The advantage here is that I can pick up a heater as and when a suitable bargain arises budget delaying the overall project. Should I just wait until I can sea-trial her and then review/retro-fit?

There is a degree of modernisation anyway in the rebuild and some 'practical' alterations for more all year UK boating. It's unlikely that the original balance will be maintained as there will inevitably be some extra weight here and there (if that's of significant importance) .

Once finished the boat will be be less speedboat and more of a compact coastal day cruiser. Albeit mostly open (with camper cover) and keeping her classic lines - also quick enough to run for refuge when needed! Whilst the Fletcher hulls have a good reputation for off-shore racing and thus capable of handling the seas, I'm looking for less speed and maximum stability. Ultimately I want to be able to cruise all around the South West (from various launch sites but mostly Torbay) with perhaps a 100 mile range that I can build towards steadily over a few seasons. She has the advantage of being small enough to trailer and sneak into all the best Westcountry inlets, rivers etc, but just about do-able for an occasional overnight/extended voyage...

Notable extra weight items will be anchor/anchor locker (not present currently, auxiliary outboard (somewhere in the 4 to 9 hp range?), extra batteries, heater (& small diesel tank), radar arch and electronics - none of which were previously fitted. If I can figure a means to fit, a chemical loo too!

Thanks in advance as always and apologies for the long waffling post!

Hi Robin,

I’m looking at updating my Fletcher 15 GTO and given how the rear end sinks when getting on the plane, I’m considering trim tabs. One other mod I’m considering is installing a fixed petrol tank and notice you’ve considered locating one in the bow, could you offer me any advice please?

kind regards Mark