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Monos built strickly for SAW?


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#226 Andy Brown

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Posted 23 December 2017 - 09:23 AM

5+ years and over 21,000 views.  Great to see the continued interest in this subject!





#227 guy leveque

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Posted 25 December 2017 - 01:03 PM

Guy,

 

You could try a brass tube as a strut with no support bracket two layers thick for support with the prop about two inches from the transom and put the rudder about an inch and a half to the right of centerline to start.  I would put the prop shaft dead center out the centerline of the keel because at high speeds the rudder will lift the right side of the boat to compensate for torque roll.  If the boat torque rolls to the right at 65 mph then move the rudder location more to the right.  As the boat goes faster the rudder will have more effect so things change every 10 mph gained.  If the boat rolls left move the rudder more to the centerline of the boat.  Each boat is different.  If the bow is buried move the prop closer to the transom.  There is no simple answer.  It takes a lot of experimentation.  More time at the pond than you might want to spend.   My 20 boat at 80 mph has the rudder almost directly behind the prop and the prop is less than an inch from the transom.  At slower speeds the boat lisps to the right.  It is a process that you need to tune to the speed you obtain.

 

John

 

thanks very much John!

 

I will keep you informed of first test run results, in a few weeks... ;)





#228 Tom Foley

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Posted 25 December 2017 - 01:51 PM

Yeah John Finch I am going to pull it down and look at it some but also thrashing for the nitro race in bran Jan 19 .



#229 Ralf Moser

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Posted 05 February 2018 - 07:27 AM

Ralf,

 

This is the way I interpret the rules............So long as the strakes are triangular shaped and don't exceed 3/4 inch wide and 5/16 inch deep they are legal.  On a standard deep vee boat they may or may not create a tunnel if close to the keel.  Depends on size of strake and vee angle of boat.  So, yes, the strakes could cause a tunnel and still be legal so long as the strakes do not protrude as low as the keel and they maintain the pie shape configuration preventing a riding surface.  A rule change would be necessary to prevent the strakes from creating a small tunnel in some configurations.  That is something that could be brought up by your district director for a rule change. 

 

 

John

Hello,

thanks for the clarification.

 

As is do this sport living in germany i do not have a district director. But the impba and namba rules do describe the mono better than the rules in germany (allowing steps, which makes monos in our small RC-dimensions defenitely a hydro as it can be setuped like hydro if being smart).

And we would like to be able to join US Saws. To my knowledge only a handful of people worldwide are doing fast mono stuff.

 

At the beginning of this thread some points were already discussed regarding overhangs.

Sadly the rules are basically clear, but otherwise it looks like sometimes there is a wide allowance of discretion. In the end the Rules are not defining all the stuff exactly.

 

Trimtabs: there is common sense putting trim tabs to a boat, typically one each side. For SAW you put them near the keel. It is also standard that you can put them above the running surface or leveled with the wetted surface.

A trimtab has to be wetted to have any sense. With that it gets automatically a running surface at high speed setups.

 

Funny consequence: with a twin you can place them nearly to the keel, see 01. You can now argue that this is a step at side view?

 

Lets do it on a boat with a ridepad, see 02.

Hm, now it is leveled to the nominal keel, if you warp it it is below the nominal hull keel. It looks legal as trimplates are working as intended: trim the boat. And only the surfaces of the hull itself are not allowed to stick out of the bottom keel.

Also keep in mind, that this is only an easy implementation of the function of a hook. Hooked boats are also standard.

 

Lets go further: why using two tabs, when only one is enough? See 03

Two things are interesting: the single tab and dual tab (like standard) are both creating the same configuration of keel alignment.

But it should be legal.

 

And now put this on a ridepad boat, see 04

You can put them above or leveled to the ridepad. Same questions as above....mounted above one can argue it is a step, leveled it is potentially below the keel of the hull itself. 

 

So..i am lost. It is a simple trimtab, used as it is supposed to be. But there are thousand interpretations possible making a boat illegal.

In the end the function of the sketched trimtabs can be simply involved in the hull. It is only more effort. 

 

Basically i think all of these sketches are legal, right? Cause hardware like a simple tab can be mounted in every position.

 

Regards

Ralf

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Edited by Ralf Moser, 05 February 2018 - 07:30 AM.


#230 wayne middlemiss

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Posted 05 February 2018 - 04:47 PM

Nothing wrong with any of those configurations depicted.

#231 John Finch

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Posted 06 February 2018 - 11:10 AM

Ralf,

 

Did you run trim tabs when you went over 100 mph?  My guess is no, because they would be out of the water at full speed.  I am also guessing you did not have a pad on the keel.  if you are looking at experimenting with the center trim tab you can go faster by just adjusting the cup or rocker in the pad by just a few thousandths at a time with a small flat file using it in a cross file configuration.  I have found very very very small strokes of a file to make the difference in the boat blowing off the water or running wet if it has a pad.  You probably already know that, so why the questions about all these configurations.  Are you looking for a better way to reduce drag or gain control? Just curious is all.  Maybe you have something already working for you and just want to see if it is legal?  Not trying to put you on the spot, just curious.

 

John


Edited by John Finch, 06 February 2018 - 11:32 AM.


#232 Ralf Moser

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Posted 06 February 2018 - 11:32 AM

Hi John, no, the old boat from 2014 had none. The current one i do also running without, but thinking about adding some. This is why the question came up.

Reading the first pages i got uncertain because of the discussion of overhangs.



#233 Ralf Moser

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Posted 06 February 2018 - 12:22 PM

Ralf,

 

Did you run trim tabs when you went over 100 mph?  My guess is no, because they would be out of the water at full speed.  I am also guessing you did not have a pad on the keel.  if you are looking at experimenting with the center trim tab you can go faster by just adjusting the cup or rocker in the pad by just a few thousandths at a time with a small flat file using it in a cross file configuration.  I have found very very very small strokes of a file to make the difference in the boat blowing off the water or running wet if it has a pad.  You probably already know that, so why the questions about all these configurations.  Are you looking for a better way to reduce drag or gain control? Just curious is all.  Maybe you have something already working for you and just want to see if it is legal?  Not trying to put you on the spot, just curious.

 

John

 

Yes, i did this stye of tuning on all my monos. Also had to do it on my new.

 

But...I am not sure what route i will go in the end. Tests have shown that the keel is in first place not critical (testet standard Vee, small Pad, slightly bigger pad). 

I am also tired about use blueprint and a file for each different lake to adjust the hull. Sometimes the sensitivity of the hull for water quality is crazy.

My hull allows me to think about some old stuff in a new arrangement.

In the end i want to reduce drag and having better control of the angle of attack.

 

This is why i added the sketches, first of getting an agreement on typical trim tab layouts, and the progress of thinking, why i expect the other arrangements to be legal :)



#234 John Finch

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Posted 07 February 2018 - 10:55 AM

Ralf,

 

I have found the trim tabs to be of use it getting the boat to ride well until it reaches full speed and then they are completely out of the water for a SAW pass.  I have used a small block of aluminum attached to the left side of the transom with a 5 degree angle also to trim a boat.  Located right close to the keel between the trim tab and keel and only 1/4 inch long in place of trim tabs with better results than trim tabs.  It trips the boat to the left (opposite to trim tabs) because it is right at the keel.  Trim tabs always slow all my boats but add control.  Filing the bottom or adding material to the bottom at the transom always gets me less drag than using trim tabs.  I have tried different vee angles as well and they all work.  Like you said......reduced drag is key.  The difference in a really fast boat rather than just a fast boat is reducing slippage at the prop.  To do that we need to reduce drag.  Unfortunately I don't see any way to reduce the angle of attack of the mono to reduce drag because it has to be one continuous wetted surface to be classed a mono.  You have done better than anyone else in reaching top speeds so I know you are wise to all I am saying but this conversation may help others to go faster with their mono hulls.  If we could use wings and steps we could come up with faster setups but then they would be classed hydros.

 

John



#235 Christian Lucas

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Posted 07 February 2018 - 03:40 PM

Hi,
biggest drag that you can tilt is the ruder. Giv it a thought to run with no ruder only vector trust and maybe aerodrag plates that can moved by servo . So some electronic needed to hold the straight and a sharp V-keel . some good thought , https://www.mentor.c...er-speed-record .
But also think about to plaze the ruder as far behind the transom as you can do on a long ruder outrigger to size the ruder as small as it can be with this long leverarm.
Are there any design or other limitation for the ruder? The turning disc ruder has less drag but gives funny moments on the boat .

Happy Amps Christian

#236 Ralf Moser

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Posted 08 February 2018 - 06:54 AM

John,

 

i understand your point. But this is already judging the performance of the implementation of the tab.

It does not answer if the sketched implementations are legal.

 

When i speak about reducing the angle of attack it is relative. Coming from high angles. Reducing the angle is not intrinsically increasing drag. The most critical point is the riding depth of the hull. 

If you have a shallow vee you will not drive as high angles of attack as with a deep vee to produce aerodynamic lift. 

 

I do not get the point of the continous wetted surface and the connection to the angle being a mono. 

If you are a lucky guy getting your mono flying on the prop (on whatever angle) it is still a mono if it fits the rules. It is only a different (and way harder) approach of well balanced aero and hydro.

 

Ralf


Edited by Ralf Moser, 08 February 2018 - 06:55 AM.


#237 John Finch

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Posted 08 February 2018 - 08:47 AM

Ralf,

 

Yes your drawings are legal.  Sorry for not answering that question.  I fear that someone might lengthen the trim tabs to the point they become riding surfaces like a hydro but I have not had to deal with that yet as mono Director.  About thirty years ago I seem to recall that

it was illegal to mount trim tabs any higher than 1/8th of an inch from the bottom of the boat but I do not see that in the rule book today.  Maybe it is a NAMBA rule?  Maybe it was taken out when the rules were re-written?  Maybe it was a local rule?  Anyway.......as the rules are written all your drawings are IMPBA legal.  While wings are illegal, aerodynamic spoilers like you had on your boat at the transom are legal.  I assume yours was to keep the boat from stuffing?  I used rails on the deck of my Wild Thing when I set a SAW record with it a couple years ago to keep air from sliding off the deck. It was something Ron Shaw suggested and it worked pretty well.

 

John



#238 Ralf Moser

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Posted 08 February 2018 - 11:58 AM

Thanks for the clarification.

 

hehe, your point about the length would be the next question: i agree that it is possible to extend a trim tab extremly (same as with drives). Even with the CoG is moved way forward someone can put the tab high and make it really long. 

This will make the length limitations of a hull nonsense and mounted them high you have a stepped boat with the CG forward the step. Not a typical approach but potentially a starting point.

 

Looks like (for me) that a trim tab length w.r.t. the hull length is helpful. Or as you said a limit in mounting height. 

I made a layout with a 5" long trimtab (boat is 39" long). 

If this tab is within this 1/8" mounting height is it legal?

 

It is not a virtual question, I built such a thing the last weeks to sort out a physical behaviour. But maybe it works....

 

This trim tab story leads to one last thing with the allowed rectangular drives: in principle you can achieve the same functionality like a long tab with such drives.

 

When i showed up with my twin boat everybody asked me "why not using rectangular drives, then you have running surfaces".

That is exactly the point: my aim is not to build a SAW-Trimaran. i would even prefer not having any drive hardware. 

This is why i used rounded hardware.

Or to describe it in mechanic layout: the minimum required volume to hold a rotating prop in place and transfer torque.

 

Correct, the wing was to settle the back of the hull. At light wavy condition the back was pushed out of the water which destroyed my first mono 2011 on a saw. With the "gurney" flap the boat gets back parallel to water surface (in the air before settling again) after pushed out in the back. Received a slow mo video of the my run in germany 2014 where this behaviour is clearly visible.

 

Ralf

 

 

 

 

 

 

 

 



#239 John Finch

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Posted 08 February 2018 - 12:28 PM

Yes it is legal.

 

John



#240 Christian Lucas

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Posted 09 February 2018 - 03:32 PM

Hi,
you are thinking on such trimtabs. Yes ,to long ,transforms a mono in a canard.

Happy Amps Christian

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