Smart Tabs

[BOAT]

All the stuff you said is all the stuff that people do to make powerboats go fast - the little tiny skeg in the middle and the lap strakes down each side - and they all work. In the Roger MacGregor thing i read he says under sail the back of the boat is just being pulled along for the ride and does not have a huge effect on the sailing part - but that under power the back part is very very important. It suggests that any improvments you make to the shape of the rear 1/3rd of the boat can have a big impact on speed under power, but it also suggests that the same modifications will not cause much problem for the sailing because apparantlu the boat sails on the front 2/3rds of the boat. I think your going in the right direction to break a speed record under power without really comprimising speed under sail.. If it works it could be a very popular new class of mods (power mods) for speed. The first thing that needds to be determined is: what IS the fasted that your motor can propel ANY boat shape of the same weight over water? That maximum is your goal because you will never reach it, but at least you will know what's possible.

We need to put an ETEC 60 on a 2000 pound boston whaler and see what the moror is capable of so you know what your shooting for, (or MERC, or whatever your motor is).

(Am I saying that right? is is MOTOR, or should I say OUTBOARD? Engine? no, not that maybe somthing else.)

[Crikey]

Very hard to do the 'before -after' thing, at this point, without going to a lot of trouble. I'd even take a slight dip in top speed if I could come away with some gains in non-WOT running, such as fuel mileage and handling. Currently, I might do 20 - 21 mph with glass conditions (and a tailwind!), maxing out my 60hp Suzuki. Turning hard, at this speed, or higher, with the mast raised has to be asking for trouble. Too much mass high up!
I'll try to give Highlander a run for his money (or Scotch) later this year, to see if I've matched his big 75hp donk.

Proofs in the pudding (are you listening John?)

R.

[Crikey]

They're on!

Thought I'd post a pre-running status report of the installation. Had I known what a hassle it was going to be re-positioning the ballast valve I might have chickened out before things got started! There was only one position possible for these baby's, which was determined largely by the stern gate mounting, and the rudder and engine port-to-starboard swing. When I took the waste gate off I found it was secured only by the screw threads biting the fiber glass. No inside nuts! What I've done looks a little funky but should work just as well as the original, and will be replaced shortly by a Valterra 12v RV equivalent for easier operation by the Admiral, as well as a binnacle status light for the geek side of me. Overall, it's pretty strong now (as long as no one steps on it!) with washers and nuts holding it on in the interior space.
They have a deployed and retracted capability that can be utilized for either power or sail.


We should be in the water soon, then I will have to tinker with the 60lb gas strut positions for getting the right amount of automatic activation.
If the crash dummy survives the test he'll report back with some travelling video shots, for your evening entertainment.
Ross.

[Crikey]

Here's a couple more pic's:


The waste gate is 3" ABS compatible (these pictures show the assembly dry-run before sealant and epoxying).
R.

[Highlander]

Looking good Ross

But thats an aufully small prop on that teeny weeny eng.

What happened to ur dorsal fins u had on the rudders ! Sharky got too them

J

[Crikey]

Looking good Ross
But thats an aufully small prop on that teeny weeny eng.
What happened to ur dorsal fins u had on the rudders ! Sharky got too them
J

John, it's not the size of the prop that counts. It's the amount of rotation!
Yes the Mako fins had to go for now as they were both on the same side due to the rudder bracket design, and the starboard side would've hit the Tab. Next edition will use a much larger pair of $35 Doel fins angled out 30deg on each side, still turning with the rudders. However, I'd have to take everything apart again. Probably won't happen this season - the Admiral would deep six me!
Get your ownership papers up-to-date for the 60 versus 75 sweepstakes this August....
Ross

[Wayne nicol]

i know this was asked earlier, but how does the hydrofoil effect the boat,i mean, i know how it works, but what are the detriments of the foil, especially as the manual say NOT to use one.
now, not stirrin', jus' enquirin!! as i really wanted to fit one, but thought there was some hidden voodoo in the boat, that we werent allowed to use one.
maybe i should just get one.- so many other things to buy, such limited funds!!!
i know they have a bad rep for coming off underway,
but couldnt a hole be drilled either side through the hydrofoil, and the metal fin, and a small bolt either side to secure them?

[Crikey]

i know this was asked earlier, but how does the hydrofoil effect the boat,i mean, i know how it works, but what are the detriments of the foil, especially as the manual say NOT to use one.
now, not stirrin', jus' enquirin!! as i really wanted to fit one, but thought there was some hidden voodoo in the boat, that we werent allowed to use one.
maybe i should just get one.- so many other things to buy, such limited funds!!!
i know they have a bad rep for coming off underway,
but couldn't a hole be drilled either side through the hydrofoil, and the metal fin, and a small bolt either side to secure them?

Wayne, it took me a bit to overcome my apprehension concerning the factory warning too. I think some of the concern deals with the foils that stick directly out to the side of the engine and how they might grab water if the boat takes a wave from the side. There would then be a further rolling force imparted to the hull - not a good thing with a raised mast carrying sail. My choice does provide some lift but not as much as the 'wings', and it was mainly the better directed thrust that really interested me. I saw this right away with the reduced 'rooster tail' and easier planing at a lower throttle setting. Steering seems to work better under power as well.This model is also clamped on without drilling, and if it does come off, at least it won't damage the outboard cavitation plate. I don't mean to disrespect other types or choices, and it can be confusing with so many designs on the market however the chine, and strake-free displacement hull like ours seems to respond well. Perhaps another model would work even better!
Bottom line - the factory once said no engine over 50hp but look how that's worked out. It's my boat, my decision, my cash and my folly - if need be. No regrets! Hopefully the 'Tabs' will further reduce some of the power squat at the stern. We'll see...
Ross

[Wayne nicol]

thanks mate!
i will be watching this thread with avid interest- really want to see how those tabs work out- i am a bit of a purist sailer, however i love my new boat, and the versatility it offers- and we also do so much motoring here anyway- with all the fishing, and all the islands etc.
we all think it blows a lot here- until you actually want to go sailing that is!!!
so now i motor, and fish, and the sailing is something special- an added bonus- really makes me appreciate it.
back to the point- so i really want to tweak my boats motoring potential!!
i love what'yer doing.

[Crikey]

Because I'm right on the cusp of beginning to test them, I wanted to add a couple of links to the ideas that got me started in the first place. Crazy as it sounds it began with my German uncle (by marriage) - now deceased - who served during the war on not only the 'Prince Eugen' but a Schnellboot squadron in the north sea. He moved to Canada after the war and retired from a working life as a machinist. The connection I made was that our planing Mac's are very similar in hull design to the German E-Boat or Schnellboot in that it was a displacement hull (rounded) that was pushed onto plane through the application of higher than normal horsepower. In their case, similar to the PT boats and MTB boats (British) of fame with 'lots' of HP!
The German approach to this kind of interdiction craft was different from what the allies went with, whose choice were hard chines - similar to today's speedboats. The evolution of the German design followed a rounded displacement hull in order to handle the rough north sea environment better. The allies confirmed this after the war ended testing captured units.
As their experience lengthened they adopted a 'wedge' into the bottom of the transom in order to compensate for the tendency of the rounded displacement hull to give way and sink too far at the rear under power. Guess what! The Mac, because of its somewhat foreshortened similarity to the same kind of hull, also 'squats' under power.
These days, the modern solution to such behavior is to add trim tabs to the rear of the vehicle - rounded hull, or otherwise. I'm hoping to confirm our Mac's can similarly benefit from such an upward force while in the powered mode - and in particular, with the self adjusting 'Smart Tabs' gas shocks instead of an expensive hydraulically operated system, while being able to preserve the purity of its sailing mode.
http://www.prinzeugen.com/DesignManufacture.htm
http://www.thehulltruth.com/boating-for ... ges.html#b
http://www.youtube.com/watch?v=tbVEbFiPJRA
I think between the incorporation of the two tabs and my outboard foil, I might equivilate to the old 'wedge' idea. Hoping to find out....

Ross.

[jbpatents]

And... what happened? No after report?

[Crikey]

You're right, I did let this go without a progress report. This year only saw two periods where I played with tab positions trying to figure out what was optimum. Normally, I have the sailing position set on the attachment bracket (up) which leaves them horizontal and doesn't give any extra drag at low hull speeds. When I began to investigate the power setting (lowered) I found they were forcing too much turbulence near the outboard lower unit at low throttle settings which, more often than not, caused the prop to cavitate excessively with a high climb in rpm's. Not good! If I had good conditions (flat) I could hole-shot it and get enough water pressure going to deflect them upward and avoid interfering with the thrust - but only just. Any pitching encountering boat wakes or waves caused problems right away, and I had to throttle off right away to regain control of the motor.
I've figured out that I have far too much resistance in the Tab gas shocks for my implementation on the MacGregor. I chose a 60lb strut, and now think the 40lb model would have been a better choice for the boat weight. Because of the modification to my ballast valve, I could not use the last two piston mounting holes on the tabs to increase the pressure supplied by the tab to the strut but when I moved the attachment point inward as far as I could go (three holes) the tabs did work better with the water pressure, but it wasn't enough to avoid damaging flow around the prop at lower speeds.
That leaves me with a re-hash before next year's running. First I'm going to get a tighter elbow on the gate valve to give me full access to all the adjustment holes. Secondly, I will bite the bullet for a pair of the lower rated gas struts. The factory states on their website they will exchange if the original choice is incorrect, but I think I've over run the 'grace' period. It's also possible that my outboard is too high for combining with this, but that's not something I can fix without adding a very expensive jack-plate to the transom.
Another mod I'm contemplating soon is positioning two chines (Smart Rails) ahead of the rudder positions, and that may positively affect the exiting water flow behind the transom that could work with the tabs. But first things first.
On a positive note, power running with the present set-up in the level sailing position does give a better flow to the prop which seems to reduce a bit of the 'squat' and help slightly with planing. The water exiting behind the transom is forced to stay flatter and not curl up until further behind the engine. Turning under power has a firmer feel to it.
Jury's still out for a final verdict.

Ross