Author Topic: Trimaran SUP  (Read 4110 times)

PonoBill

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Re: Trimaran SUP
« Reply #30 on: April 01, 2018, 11:08:45 PM »
You're probably right about the minimal bow wave with that length/width ratio. I've never found any quantitative information on narrow hulls and why they don't generate a bow wave they need to climb over, it just gets mentioned as a fact, so this feels like guesswork, but most cats and trimarans have ratios of 10-1 or greater and they still have interference drag. I read a couple of papers on interference when Mark Raaphorst built the standamaran, you could google for them, but they're a bit dense. The upshot was there isn't much you can do for a catamaran but a trimaran can have offset hulls.

There may not be a huge improvement in performance by reducing drag, but since you have a beer riding on this thing it might be worth some added effort.

The typical way to minimize interference drag other than wide hull spacing is to offset the hulls in an arrowhead pattern or some other configuration that causes most of the generated wave energy to miss the ama hulls. Your amas are very long, so that might be hard to do. I'd say try something half that length or shorter. But you could test the concept with your current amas by moving the front iako to just behind your feet and the second iako to the tail of the main hull. You could just do time trials, or if you feel all science-y drag it beside a boat with a fish scale on a windsurfing mast.

Either way it looks like great fun. Best of luck with it and keep us posted.
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PaddleSpot

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Re: Trimaran SUP
« Reply #31 on: April 02, 2018, 11:44:04 AM »
You're probably right about the minimal bow wave with that length/width ratio. 

I did a few visual tests today with a friend on absolutely flat water, at a steady cruising speed of 8.5 km/h, the bow waves are really small with a very acute angle,  and actually meet behind the iato !


Which doesn't mean there are no other hidden interferences. I can't reduce the lenght of the amas since I need this space between the iatos to paddle comfortably. But I can try a longer iato.
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PonoBill

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Re: Trimaran SUP
« Reply #32 on: April 02, 2018, 11:57:46 AM »
If you put the front Iako behind your feet you'll have lots of space to paddle, you'd have an automatic Dave Kalama stroke length limiter and the bow wave will largely miss the Ama. The most visible wave is not the only energy being transferred to the water and the angle of the most visible wave isn't the only energy path. I won't mix quantum physics with the real world, but the energy fans out from the bow--not a sum of all histories, but not a straight line either. I can't really tell from the photos since your paddle strokes are on the side with visible water, but it looks like there's an interference pattern similar to what I saw with the Standamaran.

Again, this may make no practical difference in speed, but you've gone this far with your effort, a little additional quixotic effort might yield some performance benefit.
Ponohouse is for sale: http://www.ponohouse.com
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

PaddleSpot

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Re: Trimaran SUP
« Reply #33 on: April 03, 2018, 12:06:12 PM »

PonoBill, that's what an automatic Dave Kalama stroke length limiter would bring me :-)


 
Olivier Drut
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PaddleSpot

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Re: Trimaran SUP
« Reply #34 on: April 03, 2018, 12:08:34 PM »
The platform has been quickly modified...
« Last Edit: April 03, 2018, 01:06:10 PM by PaddleSpot »
Olivier Drut
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Pierre

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Re: Trimaran SUP
« Reply #35 on: May 16, 2018, 02:00:44 PM »
I also imagined different design, so go 4 it... https://www.facebook.com/Hi.fun.hydroworks/photos/pcb.1107013132806301/1107012959472985/?type=3&theater
Tested on a 80mile river race, needs some improvement on stabilizers placement with some option with foils or single amas, let's see and try...so far it works unreal on flat water, so stable... weighs about 16 kgs /35 lbs total ,16'9'' long (5,03 m) without rudder... and 2,1 m (almost 7' wide) connected with bamboo.
« Last Edit: May 16, 2018, 02:29:40 PM by Pierre »
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TallDude

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Re: Trimaran SUP
« Reply #36 on: May 16, 2018, 02:55:54 PM »
Very cool. You are probably getting a good amount of drag from the bamboo touching the water. You can see in your photos that there is a good splash left by the bamboo.

Pierre

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Re: Trimaran SUP
« Reply #37 on: May 17, 2018, 02:43:42 AM »
Very cool. You are probably getting a good amount of drag from the bamboo touching the water. You can see in your photos that there is a good splash left by the bamboo.
absolutely right, I need to modify that problem, thinking about raising stabilizers by about 1 inch 1/2 and adding foils below...
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Pierre

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Re: Trimaran SUP
« Reply #38 on: May 17, 2018, 01:08:44 PM »
That guy was a pioneer in that matter with a modified old surfski...http://www.forumdesup.com/t163p25-proto-sup-multicoque?highlight=multicoque  last development with hydrofoils.
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blackeye

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Re: Trimaran SUP
« Reply #39 on: May 22, 2018, 10:46:26 PM »
That guy was a pioneer in that matter with a modified old surfski...http://www.forumdesup.com/t163p25-proto-sup-multicoque?highlight=multicoque  last development with hydrofoils.

The foils have to cant inward, not outward so that as the hull rolls, lift increases on the side that one wants raised, a la Hydroptre. Or curve upwards like a leeward side DSS foil in some sailboats.

Pierre

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Re: Trimaran SUP
« Reply #40 on: May 24, 2018, 07:53:44 AM »
That guy was a pioneer in that matter with a modified old surfski...http://www.forumdesup.com/t163p25-proto-sup-multicoque?highlight=multicoque  last development with hydrofoils.

The foils have to cant inward, not outward so that as the hull rolls, lift increases on the side that one wants raised, a la Hydroptre. Or curve upwards like a leeward side DSS foil in some sailboats.
agree but... when hull rolls on one side foil moves downwards together with roll direction, so incidence and lift increase so roll tends to be stopped... my intention is to use both ways: one transverse and on each side v-shaped foils... let's try!
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Pierre

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Re: Trimaran SUP
« Reply #41 on: May 24, 2018, 08:04:54 AM »
So far I added 2 small 12" T-foils 2 inches below after amas ( raised them by 1 inch)... on flat conditions those almost dont touch water and fore amas don't touch too... Still needs to improve: 2 options: 1- replace after amas by V foils ( as explained previous post)- 2 replace those 4 amas by 2 longer, will work better in open ocean conditions!
« Last Edit: May 24, 2018, 08:07:48 AM by Pierre »
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PaddleSpot

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Re: Trimaran SUP
« Reply #42 on: May 24, 2018, 08:09:11 AM »
> Tested on a 80mile river race, needs some improvement on stabilizers placement

Pierre is too modest, he ranked 23rd out of 170 SUPs on the 80 miles "Dordogne intégrale" last week, with a broken rudder, heavy rain and front wind (our trimarans are definitely not at their best upwind ).


And he forgot to mention that he built this thing in 10 days and it was his first navigation :-)





Olivier Drut
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PaddleSpot

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Re: Trimaran SUP
« Reply #43 on: May 24, 2018, 08:13:56 AM »
Pierre, it's too bad we didn't have time to compare our creatures :) I specially enjoyed the white water par of the race, the tri' is sooooooo stable.

Can't wait for my first DW !
Olivier Drut
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PaddleSpot

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Re: Trimaran SUP
« Reply #44 on: September 21, 2018, 03:28:47 AM »
Variation on a theme...

Olivier Drut
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