Subject: Re: [harryproa] Re: Proa Squared Development FPV camera vid!
From: Rick Willoughby
Date: 6/11/2011, 7:03 PM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

 

Todd

How did it go with the dagger board?

The bow down trim is mostly related to the amount of drag and how high up the CoE is.

I cannot tell if the rudders are cambered.  Even so they seem to have squarish edges.  It may be just shadow,  Any abrupt change in section shape will lead to flow separation and the water sheeting.

A cambered dagger board will reduce the drag.  Having the sail set close to and over a flat deck will reduce drag.  These things will help bring the leading bow up.  Adding more rocker on the lw hull could be counter productive but it is worth a try.  You could also try more width in the ends ie larger entry angle.  I would go for more width before trying more rocker.  Making the ww hull with say V with 10 to 20 degree deadrise might reduce drag on it as it lifts.  This is the best way to reduce wetted surface as this hull as it unloads rather than going for too much rocker.

If you add a lot of rocker to the ww hull the water will stay attached on the underside of the trailing end and get lifted up.  This will help with bow up but increases wetted surface. 

That fact that you can get this model to sail well suggests that it will sail really well in full scale but it is still at a size where other factors like surface tension come into play.   I cannot reliably model a small scale boat like this.  It would need to be about 2m long to get more representative performance results of full scale. 

Rick 
On 12/06/2011, at 6:12 AM, tsstproa wrote:

 

Second video much better wind on a higher tide. Higher tide allows me wider sailing ground with out getting into deep water or running ashore.

First half at normal spedd second half in super slow motion and back to normal speed towards end.

http://www.youtube.com/watch?v=DCxMexef2_0

Second test last night winds were stronger. New sail linkage giving me more throw and a little more positive control. Also did a three board test. Simple connection out to leeward side of leehull On board camera quit working before I tested model with the third board.

The water sheeting effect on rear board I think is in part what your saying Rick but also from what I'm seeing it looks like high side loads put on the unweighted board? Notice ride height when its the front board vs when its the rear board. Is this the effect of having an extremely low draft with an extremely light model. Nothing pressing down on rear end of boat at speed?

Even so I'm thinking a new leehull 30''square 0r 2.5'' square for the model 36'' long hull, maybe with a little deeper rocker just to keep the bottom of stem just off the water.

Todd

--- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@...> wrote:
>
> Todd
> You can mount it roughly in line with your rudders.
>
> The camera showing the rudder in your video is handy. It looks like
> the one in shot has a blunt leading edge and the flow detaches to
> form a sheet. I am very interested to see a similar shot of the keel
> you make. If you make the edges with a small radius the flow should
> stick to them without forming the sheet. The flow attaches better at
> higher Reynolds number so it will improve as you increase the scale
> and increase the speed.
>
> Gardner and I were discussing different ways to support the loads
> from the board and we came up with the idea of a brace from his
> cockpit to a the dagger board. Your loads on the model are not big
> enough to need this detail but this solution makes it simpler to
> support a full scale dagger board that has the ability to pivot up.
>
> Rick
> On 11/06/2011, at 10:42 AM, tsstproa wrote:
>
> > Thanks Rick, I pick up something locally. Swann thumb camera.
> >
> > http://www.youtube.com/watch?v=wWRXllhPiag
> >
> > Pretty happy with performance of model. The rocker leeward hull
> > might need to be alittle deeper. Might want to widen both hulls a
> > tad or at least windward hull to maybe 22''wide.
> >
> > All the mods you mention would seem to benefit for sure but add to
> > complicating the build. For now just simple box hull formsm with
> > low free board.
> >
> > I havn't added the center dagger board yet. The boat with "out"
> > boards had lots of bite. Just adding the center with the two end
> > boards just isn't appealing to me but I will do it never the less.
> > Where do you want it in line with the two inboard or outboard of
> > leehull or in hull?
> >
> > Todd
> >
> > --- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@>
> > wrote:
> > >
> > > The board does not need much rounding on the edges because it is not
> > > working through a range of angles like the rudders.
> > >
> > > I have been working on a 12% thick section with a 4% camber. So the
> > > leeward face is still slightly convex; not flat.
> > >
> > > You should be able to shift area from the current rudders to the
> > > board so total blade area is not much more than you have now.
> > >
> > > Something that might be useful for producing hands free video is a
> > > little camera like this:
> > > http://www.hobbyking.com/hobbycity/store/uh_viewItem.asp?
> > idProduct=10093
> > > It could be mounted on the boat to give a close up view of things.
> > > They will hold about 45 minutes of recording. You can edit the good
> > > bits into a smaller clip.
> > >
> > > Rick
> > > On 07/06/2011, at 9:26 AM, tsstproa wrote:
> > >
> > > > Yeah thats next I remember your discussion on toyote.
> > > >
> > > > Todd
> > > >
> > > > --- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@>
> > > > wrote:
> > > > >
> > > > > Todd
> > > > > You should test a dagger board in the middle of the hull with
> > the
> > > > two
> > > > > small rudders. Give the board a slight camber so it is
> > lifting to
> > > > > windward.
> > > > >
> > > > > Another observation I mentioned with the drive test is that
> > the boat
> > > > > crabbed sideways quite easily. A decent dagger board would
> > prevent
> > > > > this.
> > > > >
> > > > > Rick
> > > > > On 07/06/2011, at 6:09 AM, tsstproa wrote:
> > > > >
> > > > > > Development of Proa Squared along with boards tested.
> > > > > >
> > > > > > http://www.youtube.com/watch?v=DG1LuSq_CLg
> > > > > >
> > > > > > In the video the proa squared free sailing version worked fine
> > > > with
> > > > > > the single 4 1/2 sq inch with about 3- 3 1/2 sqinches of board
> > > > > > submerged. It actually tending to bear off the wind more
> > than I
> > > > > > expected with this single board down. So the bigger boards
> > where
> > > > > > not tested in single board down configuration. I proceeded in
> > > > using
> > > > > > the two of the smallest boards for two board down sailing.
> > What I
> > > > > > experienced was heavy weather helm no matter how hard over
> > boards
> > > > > > were held over they were over powered by the sail the model
> > was
> > > > > > uncontrollable shunting, sailing in a straight line
> > etc...Lots of
> > > > > > finesse required and even then very frustrating. So I
> > jumped up to
> > > > > > the second 1 1/4''x 5'' larger retangular board wha la great
> > > > > > success balanced sailing and shunting just a touch of
> > weather helm
> > > > > > coming out of a shunt . On on the hard though hands free
> > sailing
> > > > > > straight.
> > > > > >
> > > > > > With this design of craft shunting happens so fast the
> > > > advantage of
> > > > > > leaving both boards down is quit significant maintaining
> > control
> > > > > > and predictability allows me to sail faster not the other way
> > > > > > around fight helm to maintain control.
> > > > > >
> > > > > > enjoy
> > > > > > Todd
> > > > > >
> > > > > >
> > > > > >
> > > > >
> > > > > Rick Willoughby
> > > > > rickwill@
> > > > > 03 9796 2415
> > > > > 0419 104 821
> > > > >
> > > >
> > > >
> > >
> > > Rick Willoughby
> > > rickwill@
> > > 03 9796 2415
> > > 0419 104 821
> > >
> >
> >
>
> Rick Willoughby
> rickwill@...
> 03 9796 2415
> 0419 104 821
>


Rick Willoughby
03 9796 2415
0419 104 821

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