nzjetboating Web Board.

nzjetboating.com Forums => Tech Library => Topic started by: Dicko on November 07, 2012, 12:09:54 PM

Title: Small boat handling characteristics
Post by: Dicko on November 07, 2012, 12:09:54 PM
In light of a few incidents with small jet boats, I just thought it would be a good idea to share experiences and ideas on how people drive these small boats, are there any do's and dont's, have you had to change your driving style, what are people thoughts on roll bars etc.
I'm sure that Goats boat handles differently than my boat for example and he has been in some interesting places without too many problems.
 
I have found that my boat handles very precisely in shallow water, but you have to be so careful to keep an eye on your speed, I have the trigger accelerator set up on the  steering wheel and although I have found it hard to get used to I now really like it, my boat travels much further on the plane than I'm used to and because the reverse doesn't work all that well I tend to overshoot the mark when trying to pull up in a small pool.
I've found that because the boat accelerates so quickly I use short burst of speed to get through a shallow spot and then back off quickly to keep the overall speed down, one thing I did notice was that I clipped a small willow tree coming downstream with the back of the boat the tree was only 50mm in dia but it moved the boat sideways quite noticeably, a bigger boat would have flattened the tree;.

It would be interesting to hear Matt's thoughts on how his boat handled the white water as opposed to his 151.
Anyway that's my  2c worth, look forward to hearing from other small boaters and their experiences, happy and safe boating  B))T B))T

Title: Re: Small boat handling characteristics
Post by: Matthewf/Norbert/TuiDog on November 07, 2012, 16:18:18 PM
i have had a small boat (9 feet) for 10 years and some 600 hours. I dont believe the small boats are 'rolling over' because they are 'small'. There have been countless jet boat roll overs in past years of regular size, I have seen a 141 roll at lowish speed quite innocently...

there are some small boats that appear to handle dreadfully, bouncing and sliding sideways, most of the time this is 'driven around' and there lies my point.

for the vast amount of the time its all about the skipper, if you take big risks or traverse (not perpendicular) bars with relatively large stones/rocks/snags you are going to get caught someday, the rest of the time is just plain bad luck and physics not matter how careful your are. jet boating is dangerous and exciting, probably why we like it so much.

tony the attack marine/phill-on marine 11 footer handles the white water very well, quite predictable, soft riding, nose up tendency.  but in white water anything can happen anytime with zero warning. 11 footer versus 151 is really just how far you are willing to push things, the white water does look very big in a 11 footer.

so my 0.02cents is common sense and some luck will keep you right way up, as for luck you can make your own and thats all an individuals choice.



Title: Re: Small boat handling characteristics
Post by: jetdesign on November 07, 2012, 16:28:32 PM
 aAe +1

You are correct Matt
We all have to learn to drive and not take stupid risks because the little boat goes like a raped ape

Also the word might be "TRANSVERSE"?
Title: Re: Small boat handling characteristics
Post by: mof on November 07, 2012, 16:54:56 PM
Matt's "transverse" side has been discussed at length on this web board some time ago.  ;) ;D ;D

His use of the word traverse is correct however, i.e. to move across an area. The issue that appeared to cause the most recent incident was "traversing" a large stone gravel bar with the boat's axis at an angle to the direction of travel, and therefore momentum.
Title: Re: Small boat handling characteristics
Post by: jetdesign on November 07, 2012, 17:02:20 PM
Matt's "transverse" side has been discussed at length on this web board some time ago.  ;) ;D ;D

His use of the word traverse is correct however, i.e. to move across an area. The issue that appeared to cause the most recent incident was "traversing" a large stone gravel bar with the boat's axis at an angle to the direction of travel, and therefore momentum.

ahh read it wrong
I thought he was talking of TRANSVERSE loader type bars in the intake getting stuck on snags
Thanks MOF
Title: Re: Small boat handling characteristics
Post by: Dicko on November 07, 2012, 17:09:50 PM
Transverse... Hmmmm way too much information :o :o, Well said Matt, I think that because you have a small boat you tend to think you can go anywhere and therein lies a problem, every boat has it's limitations and you need to respect that.
I've shot across a couple of gravel bars at 90deg to the bar with no issues, also ran the boat 10m up the river bank to winch it on a trailer and it handled this with no problems.
Title: Re: Small boat handling characteristics
Post by: Matthewf/Norbert/TuiDog on November 07, 2012, 17:46:14 PM
stones of similar size seems to be ok most of the time, even when sliding down sideways (traversing) to draw less water. a sand patch will soon trip or flip any size boat, including laden tour boats. i'm always looking for an exit path in any situation or planning ahead, but often you just hang on for the ride, especially if riding with mof

Title: Re: Small boat handling characteristics
Post by: swifty on November 07, 2012, 20:00:23 PM
i have had a small boat (9 feet) for 10 years and some 600 hours. I dont believe the small boats are 'rolling over' because they are 'small'. There have been countless jet boat roll overs in past years of regular size, I have seen a 141 roll at lowish speed quite innocently...

there are some small boats that appear to handle dreadfully, bouncing and sliding sideways, most of the time this is 'driven around' and there lies my point.

for the vast amount of the time its all about the skipper, if you take big risks or traverse (not perpendicular) bars with relatively large stones/rocks/snags you are going to get caught someday, the rest of the time is just plain bad luck and physics not matter how careful your are. jet boating is dangerous and exciting, probably why we like it so much.

tony the attack marine/phill-on marine 11 footer handles the white water very well, quite predictable, soft riding, nose up tendency.  but in white water anything can happen anytime with zero warning. 11 footer versus 151 is really just how far you are willing to push things, the white water does look very big in a 11 footer.

so my 0.02cents is common sense and some luck will keep you right way up, as for luck you can make your own and thats all an individuals choice.




But thats 600 aussie hours )1 ,not to much ashleyness over there ::)
Title: Re: Small boat handling characteristics
Post by: Matthewf/Norbert/TuiDog on November 07, 2012, 20:07:21 PM
But thats 600 aussie hours )1 ,not to much ashleyness over there ::)
  our rivers are no where the like of the waimak but very Ashley like in fact.
Title: Re: Small boat handling characteristics
Post by: mohawk on November 07, 2012, 20:14:34 PM
little boats are safe azz in big water  OoOoO
Title: Re: Small boat handling characteristics
Post by: mohawk on November 07, 2012, 20:17:11 PM
With 250 litres of foam stuffed in them  ;)
Title: Re: Small boat handling characteristics
Post by: mohawk on November 07, 2012, 20:21:35 PM
6 inch pumps and 25 deg V dont mix well either. Soon as you bung up the unit and loose abit of thrust and try too turn it just flops on its side and goes strait ahead  ::)
Title: Re: Small boat handling characteristics
Post by: Dicko on November 08, 2012, 09:15:31 AM
What river is that Mohawk?
Title: Re: Small boat handling characteristics
Post by: Sparx on November 15, 2012, 00:19:21 AM
Rollbars ??

I have a little boat like Goats ... what are peoples thoughts on needing a rollbar for this sorta thing ??

Im thinking No because I want to be able to get under trees etc easily without getting snagged. Boat is more for exploring etc than going a million miles an hour.
Title: Re: Small boat handling characteristics
Post by: Karl on November 15, 2012, 08:47:59 AM
I agree with you Sparx.

All boats handle differently even ones the same size. Its kind of like expecting a rally car, a stock car and a circuit car to all handle the same, because hey they are all cars!!

In terms of rollover tendencies, small boats are no different to large boats. Probably the biggest determinants are the "V" of the hull, the centre of mass, and the approach speed. A shallow v and a low COG is where you want to be.

As with any motorsport get used to your equipment before you push the limits. And if you really want to push the envelope leave the passengers at home!!
Title: Re: Small boat handling characteristics
Post by: Dicko on November 20, 2012, 03:00:23 AM
Well said Karl, for me roll bars and seat belts go together, as in a sprint boat, not in an Adventure boat where you are constantly dodging willow trees, famers fences and the like. 2c
Title: Re: Small boat handling characteristics
Post by: mohawk on December 02, 2012, 15:55:24 PM
 Karl , I would expect a little boat too roll over quite easy .
 Dump all your boats on the lawn and see which is easyest too flip  l-l     
Title: Re: Small boat handling characteristics
Post by: roland on December 02, 2012, 17:51:37 PM
 aAe
Title: Re: Small boat handling characteristics
Post by: Nigel on December 02, 2012, 18:30:17 PM
biggest thing I can see is if it's a bar or  the likes is to take it straight on and not throw it sideways... going to run aground hit it straight...

saw Rolands vid of his crash and amazed where it happened ant that it ripped over....
Title: Re: Small boat handling characteristics
Post by: mohawk on December 02, 2012, 19:24:04 PM
Thats what spooked me when I fliped, I was just wizzing along at an average pace and next thing I know Im lying in the water beside the boat.
I can see it happening alot more often with the small boat craze booming like it is at the moment  pop






Title: Re: Small boat handling characteristics
Post by: Nigel on December 02, 2012, 19:25:15 PM
 aAe yip and the power and speed of some of these new boats being made
Title: Re: Small boat handling characteristics
Post by: mohawk on December 02, 2012, 19:34:01 PM
And the fact many of them have no idea what a jet boat cant do  wam
Title: Re: Small boat handling characteristics
Post by: boon on December 02, 2012, 19:49:31 PM
 aAe the more little boats come along the more we're going to see flips, spins and crashes. I think if your going to make a small boat make them very light so one person can maneuver or flip it back over if it does flip. Or put bars and really high sides.
Title: Re: Small boat handling characteristics
Post by: roland on December 02, 2012, 19:54:50 PM
i think high sides are the way to go in small boats, that'll keep a lower center of gravity,a bar at the back like the tour boats and a higher windscreen would help stop trapping people under too.
Title: Re: Small boat handling characteristics
Post by: boon on December 02, 2012, 19:57:03 PM
In terms of rollover tendencies, small boats are no different to large boats.

Not sure I agree with you on that mate...
Title: Re: Small boat handling characteristics
Post by: boon on December 02, 2012, 19:58:46 PM
i think high sides are the way to go in small boats, that'll keep a lower center of gravity.

Haha not sure I agree with that either! Higher sides will just mean that there is more room under the boat if you do flip and get trapped! And less chance of water flooding over the gunnels or transom
Title: Re: Small boat handling characteristics
Post by: roland on December 02, 2012, 20:13:18 PM
so in the interest of enlightening people of how quickly things go wrong in small boats, heres the accident video.
low speed,approx 40-50kmh,mistakes in judgment were made and ive learnt from them,kinda hard not to.

http://www.youtube.com/watch?v=_E-WAGgkPAU&feature=youtu.be (http://www.youtube.com/watch?v=_E-WAGgkPAU&feature=youtu.be)
Title: Re: Small boat handling characteristics
Post by: boon on December 02, 2012, 20:22:48 PM
Still gives me the shivers! Wish I had my camera rolling on the bow...would have made for good viewing... silly me...
Title: Re: Small boat handling characteristics
Post by: roland on December 02, 2012, 20:25:15 PM
Still gives me the shivers!

me too,think about it every day and what could have been.

Title: Re: Small boat handling characteristics
Post by: Brizz on December 02, 2012, 21:23:50 PM
I would expect a small (light) boat to flip a lot easier. A simple calc would suggest with 2 people in the weight dynamics are quite different, ie probably heavier at the front than the back.  I would theorize two  probabilities..... the back jumps when it impacts and likely causes the opposite front corner to dip and dig in. Given that I am building a larger small (light) boat I will be going back to basics when it hits the water.  practice, practice, practice, in simple situations until I am totally familiar with its quirks.  2c B))T
Title: Re: Small boat handling characteristics
Post by: Paul on December 02, 2012, 21:29:30 PM
i think high sides are the way to go in small boats, that'll keep a lower center of gravity
High sides, means more metal higher up = higher COG.

I'd suspect rollover stability is probably a lot more about beam-to-freeboard ratio, hull-V angle, and number of strakes (if any).
I'd guess you want a high ratio, low 'V' and no strakes to reduce rollover.
Title: Re: Small boat handling characteristics
Post by: Brizz on December 02, 2012, 21:54:08 PM
As a matter of interest did the offending hull have slipcoat or plastic?
Title: Re: Small boat handling characteristics
Post by: roland on December 02, 2012, 21:55:16 PM
slipcoat
Title: Re: Small boat handling characteristics
Post by: V6 on December 02, 2012, 22:52:08 PM
I'm not qualified to comment on small boats, other than wishing I had one the many times I'v been stuck. However I have had a wee bit of experience with roll-overs:
On possibly my first Club run on the Ashburton River we had two boats roll - both full size boats & very experienced drivers too. When I flipped my own boat coming out of Lady Lake Stream, it happened just as fast as in that vid, with no warning.  The common theme seems to be alloy keel impact when turning in shallows & no sideways slide - the riverbed just grabs ya.
So regardless of hull size, I appeal for everyone to be careful out there and manage your risks - an embarrassing push is a lot less painful than a roll-over!
Title: Re: Small boat handling characteristics
Post by: iceman on December 03, 2012, 16:44:59 PM
so in the interest of enlightening people of how quickly things go wrong in small boats, heres the accident video.
low speed,approx 40-50kmh,mistakes in judgment were made and ive learnt from them,kinda hard not to.

http://www.youtube.com/watch?v=_E-WAGgkPAU&feature=youtu.be (http://www.youtube.com/watch?v=_E-WAGgkPAU&feature=youtu.be)

Bloody hell, that happened  quick :o  and it didnt look as you were that far off from hitting straight on.  I think im going to stick to deep lakes and wide deep rivers for the 1st decade or so.
Title: Re: Small boat handling characteristics
Post by: roland on December 03, 2012, 18:11:47 PM
in a blink of an eye.

for a bit more reference this is the boat. see how low it sits in the water but how high out the boat we are.

(http://i513.photobucket.com/albums/t339/rolandauret/P8251519.jpg)
(http://i513.photobucket.com/albums/t339/rolandauret/P8251502.jpg)
(http://i513.photobucket.com/albums/t339/rolandauret/P8251504.jpg)
(http://i513.photobucket.com/albums/t339/rolandauret/P8251510-1.jpg)
Title: Re: Small boat handling characteristics
Post by: jetdesign on December 03, 2012, 18:16:17 PM
Do you have the major dimensions??
Title: Re: Small boat handling characteristics
Post by: CBBR on December 03, 2012, 18:17:09 PM


for a bit more reference this is the boat. see how low it sits in the water but how high out the boat we are.

(http://i513.photobucket.com/albums/t339/rolandauret/P8251519.jpg)



i wouldn't think a bench seat would be the best idea for a adventure boat either
Title: Re: Small boat handling characteristics
Post by: roland on December 03, 2012, 18:21:27 PM
Do you have the major dimensions??

sorry,dont have the boat anymore but it was a 3m.
Title: Re: Small boat handling characteristics
Post by: Eddie on December 03, 2012, 18:38:38 PM
Is this the exact same boat?

http://www.nzjetboating.com/yabbse/index.php?topic=24247.msg177732#msg177732 (http://www.nzjetboating.com/yabbse/index.php?topic=24247.msg177732#msg177732)

Report from Karl's post attached.
Title: Re: Small boat handling characteristics
Post by: roland on December 03, 2012, 18:41:21 PM
Is this the exact same boat?

http://www.nzjetboating.com/yabbse/index.php?topic=24247.msg177732#msg177732 (http://www.nzjetboating.com/yabbse/index.php?topic=24247.msg177732#msg177732)

Report from Karl's post attached.

yes,exact same boat. Ginxd or what!
Title: Re: Small boat handling characteristics
Post by: goatracing on December 03, 2012, 18:53:02 PM
Seeing as how my names been mentioned here's some of my thoughts on small boat handling/driving

-bad boat design ,most of the small boats that are being built are to stumpy across the front and all the weight is to far forward , make the hull between 8 -12 degrees if you want to boat the shallow stuff - if there is not enough room in the hull for you and the motor/unit build a tunnel out the back to keep the weight as far back as possible

-the whole idea of a small boat is to have a SLOW PLANING SPEED and to be able to STEER QUICKLY as you pick your way through the small creek/rocks

-Where is the balance/turning point on your boat?-if you can turn your boat around in its own length from full noise its set up just right-if you are going up a creek and it starts to go nowhere you have to be able to flick it around in a very small area

-scale your boat down - it is a small boat after all ,keep it light weight and easy to push around ,keep the power of the motor in proportion to the size - do you really need a 300hp jetski motor for a 10 foot boat ? - I cant talk Ive just brought a GP1200 jetski as a doner for the next boat

-if you are going to boat shallow stuff all the time put PLASTIC on the bottom

-its no use building a small boat if it doesn't handle

-its not about how fast the boat goes ,speed wont help you pick you way through a rocky section but a slow planing speed and quick steering will - but you will need some power for the rapids

Like any type of boating in a constantly changing river whether you are in a big boat or a small one you really have to be looking well ahead and be on the ball all the time. -.There is a big difference between big and small boat mishaps-small boats just bounce over rocks but the river barges with all the extra weight just plough into things

its all about practice  - get the small boat and take it up the shallows,get stuck and have a push ,find out what it and you can do ,have a crack at some skinny stuff,try to go as slow as your boat will plane.

 accidents will always happen ,its just the luck of the draw -  we could be like the other 99.9 % of the population and sit in front of the TV and wander aimlessly around the shopping malls

 B))T
Title: Re: Small boat handling characteristics
Post by: stu#71 on December 03, 2012, 19:03:06 PM
If you watch the video at 00:10secs you'll see the river has actually "run dry".  The physics of friction.

Hope no-one was hurt
Title: Re: Small boat handling characteristics
Post by: roland on December 03, 2012, 19:03:24 PM
well said goat,im gonna stick to big boats for a while now.
Title: Re: Small boat handling characteristics
Post by: Dicko on December 03, 2012, 20:08:27 PM
Well said Goat, exactly the type of info I was looking for, I think there is a real difference between Rolands boat and Goats.
Goats is definitely set up for what I call adventure boating, the green boat has a lovely paint job, not something you would want to take for a run up the Cascade river.
It's interesting to note that Rolands boat appears to be alot narrower than a 3.3m Attack Marine, I can sit three adults in mine on as bench seat and I also sit alot lower, my boat is about 1.5m wide.
Title: Re: Small boat handling characteristics
Post by: Brizz on December 03, 2012, 21:22:37 PM
Well said goat, especially the bits about "practice" and "know your boat".... Also its surprisingly hard to learn to to go slow when you should.  A lot of small boats have done a lot of miles without incident.   B))T
Title: Re: Small boat handling characteristics
Post by: Eddie on December 03, 2012, 23:24:45 PM
yes,exact same boat. Ginxd or what!

Mate, that is no coincidence. I'd be putting a roll bar on that at least.
Title: Re: Small boat handling characteristics
Post by: johnmead on December 04, 2012, 07:37:00 AM
Well said goat, especially the bits about "practice" and "know your boat".... Also its surprisingly hard to learn to to go slow when you should.  A lot of small boats have done a lot of miles without incident.   B))T
+1 That bit about "learn to go slow" if very important in all size boats, especially going downstream. It is so easy to "gun it a bit" fos a sckinny spot, and then forget to lift the foot again. After two or three skinny bits, you suddenly find you're going too damn fast for the next bit  C"" C"" 
  Have a safe summer everyone
Title: Re: Small boat handling characteristics
Post by: CBBR on December 05, 2012, 19:31:28 PM
+1 That bit about "learn to go slow" if very important in all size boats, especially going downstream. It is so easy to "gun it a bit" fos a sckinny spot, and then forget to lift the foot again. After two or three skinny bits, you suddenly find you're going too damn fast for the next bit  C"" C"" 
  Have a safe summer everyone

cant b that skinny if you not scrubbing your speed while sliding across the bottom  ;)

its called controlled aggression, enough momentum to get thru but not too much it gets you in trouble
Title: Re: Small boat handling characteristics
Post by: mohawk on December 05, 2012, 20:45:19 PM
Mate, that is no coincidence. I'd be putting a roll bar on that at least.
There are alot of those hulls around and many very similar which dont roll over every second time their used  ::) .
There aint much you can change in 3 metres of boat and adding a roll bar and no belts only raises the COG more and increases the danger.
Id lower the seating for sure in the green boat (because it looks silly sitting way up there like that ) but as Ive found with mine sitting too low makes it real hard too see in the shallows so I sit up on my roller and youd be surprised how much the boat seem too lean over in the turns.
 Regardless of deadrise , COG , or design  .. their light and fast and sooner or later like all the best things in life they will leave you broke or broken  l-l
Title: Re: Small boat handling characteristics
Post by: heemi.v8 on December 20, 2012, 18:32:16 PM
so in the interest of enlightening people of how quickly things go wrong in small boats, heres the accident video.
low speed,approx 40-50kmh,mistakes in judgment were made and ive learnt from them,kinda hard not to.

http://www.youtube.com/watch?v=_E-WAGgkPAU&feature=youtu.be (http://www.youtube.com/watch?v=_E-WAGgkPAU&feature=youtu.be)
Holy chit. That's scary. Glad you guys are ok. After observing this footage and how it grabbed in the shallow small pebbles I have to admit that i have felt the same tendencies with my boat. A warning to the many people with my plans. Will be experimenting a little more in the spring. Be careful people. I recommend a roll bar and seat belts. And it doesn't have to look bad.
Title: Re: Small boat handling characteristics
Post by: heemi.v8 on December 20, 2012, 18:33:02 PM
so in the interest of enlightening people of how quickly things go wrong in small boats, heres the accident video.
low speed,approx 40-50kmh,mistakes in judgment were made and ive learnt from them,kinda hard not to.

http://www.youtube.com/watch?v=_E-WAGgkPAU&feature=youtu.be (http://www.youtube.com/watch?v=_E-WAGgkPAU&feature=youtu.be)
Holy chit. That's scary. Glad you guys are ok. After observing this footage and how it grabbed in the shallow small pebbles I have to admit that i have felt the same tendencies with my boat. A warning to the many people with my plans. Will be experimenting a little more in the spring. Be careful people. I recommend a roll bar and seat belts. And it doesn't have to look bad.
Title: Re: Small boat handling characteristics
Post by: boon on December 20, 2012, 20:27:15 PM
I recommend a roll bar and seat belts

 b>  b>