Hobie Cat Forums

It is currently Sun Dec 21, 2014 5:13 am

All times are UTC - 8 hours [ DST ]




Post new topic Reply to topic  [ 52 posts ]  Go to page Previous  1, 2, 3, 4  Next
Author Message
PostPosted: Wed Dec 07, 2011 10:42 am 
Offline
Site Rank - Captain

Joined: Wed Nov 30, 2011 11:53 pm
Posts: 31
frisbee wrote:
I saw an outback just the other day being towed by an aircraft carrier (don't ask what aircraft carrier. I am not allowed to disclose the particulars.).
When the outback's speed approached the maximum speed the hull would allow per some weird formula what Happened?
A) the aircraft carrier's anchor chain that was used as the tow chain Snapped from the strain.
B) the Outback became longer as the speed increased ( a new take on the Theory of relativity. I discussed it with Albert and he was amused.)
C) the outback became the Delorean in Back to the Future, and the rider went back to the days when there were no legal limits on inshore fishermen (Minus the fire streaks on the water)
D) The outback went as fast as the aircraft carrier pulled it.
E) No matter how hard the Aircraft carrier tried it could not overcome the hull limitations of the Outback, and even at full throttle the aircraft carrier could not go faster than 7.rediculous MPH.


Roadrunner
Could you tell me if the answer is not "D" then why? :|

And that hull speed formula...could you plug in the waterline hull lengths of the Hobie hardbodied, mirage drive vessels to the hull length formula and post the maximum speeds for each.... It would help to see if anyone has broken the Hull barriers.


But the real issue here was not the all important hull length rule that IS important for sailing events. The real reason that the guy's hobie wasn't going faster was because the hobie didn't offer enough resistance to impeded the maximum performance of the prop, and virtually the same propeller was on all three trolling motors. The larger trolling motors could probably put a PA on plane IF it had the right prop on it. Props on trolling motors are designed to move big boats slow. If osmeone got off their butts and designed a prop to maximise speed for a PA it'd be a beast, and a real headturner. I bet their are better props than the stock ones on trolling motors already out there on the shelf. Anyone?
It was the mismatched prop that cause the poor performance of that vessel with the larger motors.


Top
 Profile  
 
PostPosted: Wed Dec 07, 2011 11:01 am 
Offline
Site Rank - Captain

Joined: Wed Nov 30, 2011 11:53 pm
Posts: 31
or is all we are arguing about is if the 55lbs with the right prop could get the Kayak on plane?


Top
 Profile  
 
PostPosted: Wed Dec 07, 2011 11:04 am 
Offline
Site Rank - Captain

Joined: Wed Nov 30, 2011 11:53 pm
Posts: 31
could be these props could make the yak go faster with a decent powered trolling motor
http://kipawapropellers.com/

But personally I am looking at the Watersnake Saltwater 18lbs of thrust for a "fishing aid".
http://watersnakeusa.com/motors/transom/asp.html


Top
 Profile  
 
PostPosted: Wed Dec 07, 2011 2:27 pm 
Offline
Site Rank - Old Salt

Joined: Tue Jul 19, 2005 6:29 pm
Posts: 2096
Location: High Point, NC
The difference between the freshwater and saltwater versions is the color of the paint. That's all.

It's the same model as the 18lb thrust Sevylor which you can get on Amazon. Exact same motor. Identical.


Top
 Profile  
 
PostPosted: Wed Dec 07, 2011 11:20 pm 
Offline
Hobie Approved Guru

Joined: Sat Nov 12, 2005 10:46 pm
Posts: 2424
Location: Escondido
frisbee wrote:
D) The outback went as fast as the aircraft carrier pulled it.
Could you tell me if the answer is not "D" then why? :|
Actually the eddy from the carrier would suck the Outback right up to the stern. Ignoring that, D would be right for a couple of reasons.

1. The traditional formula was derived for large displacement hulls, primarily navel vessels. Kayaks and most light boats have semi-displacement hulls. So the 1.34 formula does not fully apply. "Hull speed" is still there, but the old formula has been more accurately replaced by a Froude number -- it can vary greatly from one boat design to another.

2. The aircraft carrier has ample power to easily pull the Outback out of its wave trap. As a practical matter though in the trolling electric motor world, simply doubling the power doesn't get you nearly enough to break out of the wave trap. That is what I was addressing originally.

In this picture series you can see the wave trap developing as the PA goes faster. Note how much the stern is squatting in the lower picture:

Image

Image

Quote:
And that hull speed formula...could you plug in the waterline hull lengths of the Hobie hardbodied, mirage drive vessels to the hull length formula and post the maximum speeds for each.... It would help to see if anyone has broken the Hull barriers.
The "hull speed" zone is easier to exceed in some boats than others. Generally the beamier the boat (for a given waterline length) the bigger the bow wave, the deeper the wave trap, the harder to escape with more power. Other factors come into play as well such as rocker for example. The PA, Outback and Outfitter generate big waves near "hull speed" and have a relatively hard speed limit (without lots of additional power). The Adventure, being longer and narrower, has a much softer limit so the "climb" out of the trap is much gentler and it takes less additional power to go faster.

All the Hobies can exceed hull speed -- it's only a matter of how far and how much thrust is available.

Quote:
But the real issue here was not the all important hull length rule that IS important for sailing events. The real reason that the guy's hobie wasn't going faster was because the hobie didn't offer enough resistance to impeded the maximum performance of the prop, and virtually the same propeller was on all three trolling motors. The larger trolling motors could probably put a PA on plane IF it had the right prop on it.
It was the mismatched prop that cause the poor performance of that vessel with the larger motors.
You may be right. No doubt the prop has to match the application and it may well be as you said that the prop was topped out at that speed.

But the same result occurs when the boat approaches its hull speed. The bow wave gets so big the power needed to climb up and over-power it is generally not available on our kayak realm regardless of prop pitch. If you notice on the water, the only small boats you usually see going much faster are planing hulls, foils and multi-hulls. For the record, some small sailboats can beat the snot out of any of the Hobie kayaks -- they don't suffer any unique hull speed limitations IMO.

Hope this helps. 8)


Top
 Profile  
 
PostPosted: Thu Dec 08, 2011 5:46 am 
Offline
Site Rank - Old Salt

Joined: Tue Jul 19, 2005 6:29 pm
Posts: 2096
Location: High Point, NC
In other words, boats are not limited to their ascribed "hull speed." They can go as fast as you're able to push them (and there is a difference between pushing and pulling one).

You can continue pushing a boat faster until such point that you can no longer pilot it in a straight ahead line. At that point, you've taken it as fast as it can go.


Top
 Profile  
 
PostPosted: Thu Dec 08, 2011 10:01 am 
Offline
Site Rank - Captain

Joined: Wed Nov 30, 2011 11:53 pm
Posts: 31
agree agree agree.


Top
 Profile  
 
PostPosted: Thu Dec 08, 2011 10:02 am 
Offline
Site Rank - Captain

Joined: Wed Nov 30, 2011 11:53 pm
Posts: 31
But I sure would like to see someone getting close to the edge in some sit on yaks


Top
 Profile  
 
PostPosted: Thu Dec 08, 2011 10:02 am 
Offline
Site Rank - Captain

Joined: Wed Nov 30, 2011 11:53 pm
Posts: 31
or over the edge :D


Top
 Profile  
 
PostPosted: Sun Dec 11, 2011 8:44 pm 
Offline
Site Rank - Deck Hand

Joined: Sat Oct 22, 2011 12:28 am
Posts: 20
I am interested in seeing some examples of gas outboards on hobies. Here is a Hobie Pro Angler with a gas outboard going pretty fast:



Top
 Profile  
 
PostPosted: Mon Dec 12, 2011 6:27 am 
Offline
Site Rank - Old Salt

Joined: Tue Jul 19, 2005 6:29 pm
Posts: 2096
Location: High Point, NC
That's about 7MPH - not at all bad but a lot of trouble to go to in order to pick up a single MPH over a good electric set-up.


.................


Top
 Profile  
 
PostPosted: Mon Dec 12, 2011 10:25 am 
Offline
Site Rank - Old Salt

Joined: Sun Apr 20, 2008 6:18 am
Posts: 1442
Location: Sarasota,Key West FL
eclipse504:
I think that 5hp merc comes with a low pitch prop (designed to push a 2500 lb boat). If he puts on a higher pitch prop, he should be able to get 15 mph (edit 10-12 mph on unmodified motor).

I have a 2 hp gas on my TI (which is much larger than the PA), with my 7 inch pitch prop I can get 5 mph, but the motor cannot get to top RPM so that's about it (not enough HP).
With that 5hp listening to it on the video, he is no where near being maxed out on the HP. What is limiting his speed is his low pitch prop.

Bob


Top
 Profile  
 
PostPosted: Fri Dec 16, 2011 7:00 pm 
Offline
Site Rank - Captain

Joined: Sun Jul 03, 2011 5:58 am
Posts: 47
Jollymon wrote:
I just don't understand why people put motors on their kayaks. Defeats the whole purpose.

Jolly

The only 'purpose' i see is to get our fat arses off the couch and outside.

Not looking for simpathy here. We bought our Oasis this summer as i recovered from a crushed femur due to a motorcycle accident. I couldnt use the drive then and might not ever but we have them.

I recently installed a trolling motor to get out fishing. On the shake down (~1.5 hrs) it barely touched the battery. I wouldnt have been able to say the same if i had to paddle.

By design these things are modified to our own needs. As i am new to this type of recreation i would hope that the white water yak crowd doesnt scoff at our fishing outfits. Why show distain for a mod when you dont know the facts or needs behind it?

Having to register the Yak once 'propulsion' is added is just revenue and doesnt reclassify anything.

Hope to meet you on the water and share the adventure.

Steve
Virginia Beach


Top
 Profile  
 
PostPosted: Fri Dec 16, 2011 7:07 pm 
Offline
Site Rank - Captain

Joined: Sun Jul 03, 2011 5:58 am
Posts: 47
Quote:
What is limiting his speed is his low pitch prop.

Bob


And that freeloading lump he is dragging. :D


Top
 Profile  
 
PostPosted: Thu Feb 02, 2012 11:17 pm 
Offline
Site Rank - Captain

Joined: Wed Jun 09, 2010 2:16 pm
Posts: 32
Jollymon wrote:
I just don't understand why people put motors on their kayaks. Defeats the whole purpose.




When fishing long distances in a larger river, the Evolve motor can get you more distance with less effort if the current is particularly stronger than normal


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 52 posts ]  Go to page Previous  1, 2, 3, 4  Next

All times are UTC - 8 hours [ DST ]


Who is online

Users browsing this forum: Yahoo [Bot] and 3 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group