# Hobie AI - is 'submarining' a problem in lumpy seas?



## Shufoy (May 28, 2008)

Heya Mike,

The submarining is not so much a design "flaw" but more a trait of that type of flat, rockerless hull that is featured in the Adventure. It has many benefits, that far outweight this trait, such as higher hull speed with longer waterline length, better glide, better penetration into chop, tracks straighter. If you look at high performance ocean racing yachts they resemble the adventure hull shape to some extent, and also exhibit the same submarining traits.

With the AI the submarining is just the extra horsepower of the sails exagerating an already present trait of the Adventure in its penetration through chop, and the extra drive of the sails pushing it further thru the wave before it rises up and thru, creating the submarining. It is also very noticeable in a following sea, as you overtake the waves, drop into the trough between and the nose penetrates into the next wave.

The wave deflector i fitted massivley reduced this trait, not entirely getting rid of it, but it stopped the nose going in in a lot of cases, and when it does, pulls it up quicker.

Hope this helps mate.


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## Rhino (Dec 17, 2007)

Great answer Brett.


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## RedPhoenix (Jun 13, 2006)

Unfortunately, due to the change in ownership of this web site and the lack of response by the owners to my requests to remove my email address from all administrative-level notifications and functionality, I have decided to remove my posts on AKFF. Thank you for the great times, the fantastic learning experiences and the many many fish. If you are desperate for the old content of this particular post, it is available below base64 encoded and bzip2 compressed.

Red.

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## Shufoy (May 28, 2008)

Thanks Darren!

Mike the wave deflector is easy to fit, most aussie kayak manufacturers make a similar product to the Finn Kayaks one that i used, so see if theres a local manufacturer in your area. Failing that, if youre chasing one, give me a yell and i'll arrange it.

I'll put some pics up when i get home, but this vid should tie you over, it shows a great example of submarining!!


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## sitonit (Dec 29, 2006)

Why did you add the nose piece to correct this trait?


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## Sunhobie (Jun 22, 2006)

Spray deflectors on sailboat bows are generally considered bad design. The very idea of modern bow shapes is to allow them to go thru waves,and shed the water,rather than bulldoze thru every wave, shedding speed in the process. Deflectors can catch water on their upper surface when they submerge and then act like a jammed front brake on a pushbike. Sure, the AI submarines a bit, when it hits the bottom of a swell, especially with plenty of sail up, running downwind. There is quite a bit of rotational force exerted by sail area 5m up in the air.

Now that some of you blokes are becoming part-time grotty-yachties, you will need to learn some old yachtie tricks:

1. *Reduce sail to go faster*. It seems crazy, but when the wind pressure starts to cause uncomfortable characteristics like nosediving, submarining, outrigger submersion, rolling up (furling) some sail will actually make the boat quicker. This is because smaller sail means lower centre-of-effort and therefore less leaning, as well as less tendancy to dig the nose in.All Yachts reef their sails when the wind gets strong.

2. *Distribute weight to improve trim*. If you know you are going to be doing some strong down wind sailing, put all your heavy gear inside the hull, behind the seat, not in the front hatch. You can even lean back a bit in the gusts, if you loosen your seat straps. Even maxi yachts stack all the crew at the "back of the bus" when running hard before the wind, to improve handling.

3. *Pull up your daggerboard.* The drag, caused by a daggerboard can accentuate the bow-down problem at high speed. (In our fast catamarans, we must pull the daggerboards all the way up down wind, otherwise we trip over them because of tip drag .) Likewise, having the mirage drive fins up against the hull helps. Removing it altogether and using the cassette plug is even better.

4. *Improve your sail handling* In strong wind, don't just turn the boat into gybes, with the mainsail all the way out. Rather, wait until the boat is at full speed, pull the mainsheet to the centre "blading the main", and then turn gently and let the main run out as the sail flips through. This reduces the occurrence of broken rudder pins also.

Believe me, I have experience with nosediving. I have hit the p*ss at over 25kts, whilst double trapezing on a Hobie Cat many times. Nosediving just happens on all sailboats. Some just slow down and fall over. The faster ones can completely trip over themselves. I have sailed the Island in very strong winds and big seas. It is a wet ride, thats life. I reduce the sail to make it more comfortable.


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## Shufoy (May 28, 2008)

RedPhoenix said:


> Not really too much of a problem though - only significantly noticeable when you're in reasonable wind, going with the waves.
> 
> Red.


Spot on there Red, and this is really the only reason i fitted mine, as we are usually going out with the wind behind us and coming in the same.

Some good points there too Mal, the Wave Deflector, bad design or not tho does go a long way to reduce the "submarining" effect, it may also, in doing so reduce performance a tad, but barely, if at all noticeable on an AI, would mabye be noticeable on a high performance boat, if it even had one. I personally think it is a benefit more than a hindrance, as whilst it may stop some amount of wave penetration, this IS what its designed for, and the fact that when you do submarine, it pulls it out that much faster, getting it back to speed quicker. You'd also be suprised how much spray it stops too.

But hey, don't believe me, they are cheap as chips, but one, fit it, and try it yourself. As a side benefit, try surfing the Adventure with one fitted, HUGE improvement!!


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## RedPhoenix (Jun 13, 2006)

Unfortunately, due to the change in ownership of this web site and the lack of response by the owners to my requests to remove my email address from all administrative-level notifications and functionality, I have decided to remove my posts on AKFF. Thank you for the great times, the fantastic learning experiences and the many many fish. If you are desperate for the old content of this particular post, it is available below base64 encoded and bzip2 compressed.

Red.

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## koich (Jul 25, 2007)

Gatesy said:


> and there is no feeling of more helplessness when you get tea bagged


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## Scott (Aug 29, 2005)

koich said:


> Gatesy said:
> 
> 
> > and there is no feeling of more helplessness when you get tea bagged


Classic


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## Buff (Dec 31, 2005)

Don't have a AI or TI so cant comment on any of its issues, but just spotted this "Solid fiberglass-built wave deflectors"
Don't know if its of any help :?


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## yankatthebay (Dec 14, 2007)

I am glad someone else asked this question. I put the fact mine did it down to "I must be too fat", but I guess that might not yet be the case.


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## Bart70 (Jan 28, 2007)

Sunhobie said:


> Spray deflectors on sailboat bows are generally considered bad design. The very idea of modern bow shapes is to allow them to go thru waves,and shed the water,rather than bulldoze thru every wave, shedding speed in the process. Deflectors can catch water on their upper surface when they submerge and then act like a jammed front brake on a pushbike. Sure, the AI submarines a bit, when it hits the bottom of a swell, especially with plenty of sail up, running downwind. There is quite a bit of rotational force exerted by sail area 5m up in the air.
> 
> Now that some of you blokes are becoming part-time grotty-yachties, you will need to learn some old yachtie tricks:
> 
> ...


Being a competitive small craft sailor in previous years what you say makes much sense - the AI does performs exactly as any small multi hull sailing vessel does. People who own one need to apply a little sailing theory to their yakking skills to get the best out of them.

For those who think nosediving is scary......try running downwind in 20+knots of wind riding a Scow Moth and you will soon realise that nosediving is a part of sailing and there are skills and practices to reduce it occurring.

Cheers,

Bart70


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## RedPhoenix (Jun 13, 2006)

Unfortunately, due to the change in ownership of this web site and the lack of response by the owners to my requests to remove my email address from all administrative-level notifications and functionality, I have decided to remove my posts on AKFF. Thank you for the great times, the fantastic learning experiences and the many many fish. If you are desperate for the old content of this particular post, it is available below base64 encoded and bzip2 compressed.

Red.

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## Bart70 (Jan 28, 2007)

I actually learnt to sail on a Scow Moth......taught me a lot about balance with a huge sail area and a hull design with a shovel nose! Downwind legs in blustery conditions would often see the nose down and water up to the mast step while I was hanging off the back to try to keep her nose up!! Not practical to move to the rear of an AI hull - but very practical to furl enough so that the hull does not go under, hull drag reduced = faster speed.

I never progressed to a Skiff Moth (similar to the one in Red's pic - but they did not 'foil' them in those days). The Skiff was just wayyy too sensitive with about 6 inches of wetted hull width!

These days they are into 'foiling' which is what you see in Red's pic and below - the entire hull lifts up out of the water and rides on the foils. I believe they will do this at about 7 knots....and are capable of in excess of 22 knots. I have attached a pic below of a Scow doing the same - awesome stuff.

If I had the agility of my youth I would get hold of one and and try to master it - they look like a huge amount of fun!





































Bart70


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## RedPhoenix (Jun 13, 2006)

Unfortunately, due to the change in ownership of this web site and the lack of response by the owners to my requests to remove my email address from all administrative-level notifications and functionality, I have decided to remove my posts on AKFF. Thank you for the great times, the fantastic learning experiences and the many many fish. If you are desperate for the old content of this particular post, it is available below base64 encoded and bzip2 compressed.

Red.

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## Slacker (Mar 19, 2009)

Awesome pics there bart70...

A whole lot of fun there... and potentially a whole lot of hurt!!

cheers

SH


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## dunno (Feb 10, 2010)

Great answers here, especially relevant is to furl the sail and pull up the centreboard. Aside from that lean back mooorree!!


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## ELM (Jul 14, 2008)

Mal thanks for the dagger tip down wind, the only one of what you suggested that I had not tried and makes so much sense when you here it, furling in some sail is a huge advantage in performance and limiting deep wave cutting.


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## ammo (Apr 18, 2010)

Some valuable gems in this thread. Thanks!


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## Bart70 (Jan 28, 2007)

RedPhoenix said:


> Stuff it - stick hydrofoils on the outriggers. Solves the nose drop issue nicely.
> 
> Red.


Hobie has actually toyed with this previously - I have attached a pic of the Hobie Trifoiler. Capable of foiling at 2 x windspeed and generating force at 2G's in corners.

215sq ft of sail, 22ft long. They produced approx 200 of them before ceasing production around 2005.

Bart70


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## Sunhobie (Jun 22, 2006)

I sold one of these a few years ago and fortunately, I got the chance to try it out. It was absolutely amazing. The speedo in the cockpit was banging on the stops at 35mph, in only 15kts of wind!!!! It went so quick, that it could barely manage to make any ground up wind!


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## spottymac (Aug 29, 2005)

Has there been any update on the Wave Deflector for the AI, 
Red was looking at getting some made in Sydney for the AI and Shufoy said the one from Finn fitted the AI OK, 
I looked at the Ocean Kayaks wave deflector and it isn't deep enough to fit over the front of the AI with out Mods,
It looks like the one from Finns is the only one at this point in time that will fit and I am hope we can hold of,


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## RedPhoenix (Jun 13, 2006)

Unfortunately, due to the change in ownership of this web site and the lack of response by the owners to my requests to remove my email address from all administrative-level notifications and functionality, I have decided to remove my posts on AKFF. Thank you for the great times, the fantastic learning experiences and the many many fish. If you are desperate for the old content of this particular post, it is available below base64 encoded and bzip2 compressed.

Red.

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## Rhino (Dec 17, 2007)

Splash Kite:


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## andybear (Jan 15, 2006)

Hi all,

I reckon a wave deflector would be a nice bit of kit!....non essential but nice.

cheers all andybear


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## Sunhobie (Jun 22, 2006)

At the start of the clip, the bow is often submerging and throwing spray. Later in the clip, with the miraculous wave kite fitted, the bow hardly dips. Must be the aerodynamic lift ;-)


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## murd (Jan 27, 2008)

After sussing out the probs youse AI guys seem to have with spray why don't you try what I have on the Loon?

I've had spray deflectors on my fishing SIKs for the past 18 years. They won't stop a nose dive but will prevent a lot of that side spray I can see in the video. This is how I converted my sik from a 'calm water' craft into an open ocean machine!

Rick


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## spottymac (Aug 29, 2005)

I have contacted Finn and they can post me a wave deflector at a very reasonable price so I am going to give it a go,


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## Lumpy (Oct 31, 2009)

I am with Mel on this one, wave deflectors dont seem like a good idea to me. Further more nose diving for the AI is more of a characteristic than a design flaw, it is still just a kayak not a sail boat. I have had my AI for some time now and I love it! The nose diving happened to me awhile back and all that happens is the boat does is slow down for a bit and then soon picks up speed again. Did not even get water in the hull!
Hear is a video of when I did some submarining.


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## Shufoy (May 28, 2008)

spottymac said:


> I have contacted Finn and they can post me a wave deflector at a very reasonable price so I am going to give it a go,


Finn are great to deal with, and big supporters of our forum over west. Heres a better pic of how i cut the sides away to make it fit. I also spray waxed the front of the hull before fitting, then used selley's all clear to "blend" the hull to the addition, let it dry, now it's a permanent fixture to the nose cone. Just use the two screws on the handle at the front to hold it all on, you can still have the handle there as well.


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## spottymac (Aug 29, 2005)

Thanks Shufoy for the pic, 
I received my wave defector from finns yesterday and spent a few hours nutting it out how best to fit it, It didn't look easy but there is nothing like a challenge, 
This is what I came up with, it looks good from the top but not the best on the under side,

I like the way you have cut back and trimmed the bottom up on yours its a much better fit so back to the drawing board for me and I will have another go tomorrow,


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## spottymac (Aug 29, 2005)

Today I trimmed back the wave deflector after looking at what Shufoy showed in the pic and I am happy with the end result,
It looks like it will be blowing 15 knot tomorrow so will give it a go,


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## RedPhoenix (Jun 13, 2006)

Unfortunately, due to the change in ownership of this web site and the lack of response by the owners to my requests to remove my email address from all administrative-level notifications and functionality, I have decided to remove my posts on AKFF. Thank you for the great times, the fantastic learning experiences and the many many fish. If you are desperate for the old content of this particular post, it is available below base64 encoded and bzip2 compressed.

Red.

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## spottymac (Aug 29, 2005)

$110.00 postage included,


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## spottymac (Aug 29, 2005)

Headed off shore out through the Gold Coast Seaway to test the new wave deflector and side spray skirts at 12 o'clock today, 
Awesome what a buzz 8) 
There was only one other boat out there a big sailing yacht.
I traveled 15km, Average speed 8.4km, Top 19kmh, Wind SE 18 knots, Waves 2.2 M and under full sail, 
What a HOOT to be out there in a AI, Thank you Hobie,
The side skirts and wave deflector made a big difference in reducing the amount of water coming over the front, 
I didn't have any submarining problems so it looks like the wave deflector is doing its job,   
My Pentax WP camera has stuffed up so can't give you any video footage until I get a new one,


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## Sunhobie (Jun 22, 2006)

Shufoy said:


> spottymac said:
> 
> 
> > I have contacted Finn and they can post me a wave deflector at a very reasonable price so I am going to give it a go,
> ...


Have you considered what will happen when you run into something and tear the whole bow (including the embedded handle inserts) off?


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## yankatthebay (Dec 14, 2007)

Sunhobie said:


> Have you considered what will happen when you run into something and tear the whole bow (including the embedded handle inserts) off?


I agree, it would seem to me that the structure of the kayak might not be designed to take such a large load at that point. I will leave mine as it is and put up with the problem...put the livewell in the back, the extra weight back there will help raise the front.


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## Shufoy (May 28, 2008)

Sunhobie said:


> Shufoy said:
> 
> 
> > spottymac said:
> ...


No. Frankly i think i am capable enough to not run into something. It's not really something that happens, ever.


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## wfish (Sep 17, 2008)

What happens once the nose goes under with a wave deflector/spray skirts on. Will they act like a shovel and dig the nose in even further and maybe end over end it. If there is a bit of the right size swell with the right gap between the waves this may be a problem. I just take the water over the bow and love it as part of AI sailing.
Wfish


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## yankatthebay (Dec 14, 2007)

wfish said:


> What happens once the nose goes under with a wave deflector/spray skirts on. Will they act like a shovel and dig the nose in even further and maybe end over end it.


if you get to that point, it wont make any difference whether you have deflector/skirts - you are in deep shit either way.


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## ELM (Jul 14, 2008)

Personally, I would rather have two sets of angled rib/deflectors running from the top of the deck, down over the and half way down sides. A final V shaped nose mounted in front of the hatch, again with an angled rib/deflector that will allow the bow to pierce the waves, but will then supply lift to the bow as the deflectors push against the rising water.

I started to make a paper mache mould of my bow with vacuum hose connections, as I intended to router some ribs and then drill a set of small holes so I could refit the mache, heat the hull from inside and vacuum form the ribs. I decided against it as I began to worry about the thinned plastic, where it would be stretched to form the rib, and then the bow flexing possibly crack through the rib.

I would now like to just make some ribs and then glue them to the bow instead.


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## cajpete (Apr 20, 2011)

Hi guys,

A couple of questions.
1. Is the nose of the AI the same as the Revolution?

The reason I'm asking is that I often nose dive on the return in surf.
Yes, I use the broadside-paddle dig technique. But sometimes the nose
is pushed back down the wave and inevitably digs in.

2. How would you attach a wave deflector like the Finn as shown in video?
Is it detachable?

Cheers, Pete


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## RedPhoenix (Jun 13, 2006)

Unfortunately, due to the change in ownership of this web site and the lack of response by the owners to my requests to remove my email address from all administrative-level notifications and functionality, I have decided to remove my posts on AKFF. Thank you for the great times, the fantastic learning experiences and the many many fish. If you are desperate for the old content of this particular post, it is available below base64 encoded and bzip2 compressed.

Red.

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