hullabaloo
Well-Known Member
I will give it a go. thanks
ps I may be back for more of you local knowledge.
ps I may be back for more of you local knowledge.
Jet Ski and boat collision - Calshot - afternoon Monday 7 May 2018 - 2:30pm ish
- Thread starter girlofwight
- Start date
BruceK
Well-Known Member
You'd be most welcome to join me, us, the crowd sometime / whenever you wish. Im out most weekends and spend most of it on the hook somewhere on the island
MapisM
Well-Known Member
Define "require".
If you mean that it's possible to build a boat whose AoA remains constant through her whole P speed range without using tabs, we can debate till the hell freezes over about whether theoretically such possibility exist. But factual evidence shows that no boat afloat behave like that. None, nought, nada, nothing, nil, zero.
Yours included, of course: as you know, I've never been onboard her, but I'm happy to bet a case of your preferred champagne that she's no exception.
Bigplumbs is 100% correct, though: we are way o/t with this, so I'll refrain from commenting in more details on the drawings you posted.
Happy to contribute as much as I can if you wish to start a specific thread, though. :encouragement:
darryl_g
Member
I was chatting with the attendant at the Port Hamble fuel pontoon on Tuesday & he mentioned the incident.
He'd been working at Hamble Point on Monday.
He indicated that Jet Ski was heading across MOBO's bow. Rider jumped (or fell) off. MOBO swerved to avoid rider and hit the jet ski.
Major damage to one of the mobo's drives and water coming into engine bay so had to have an emergency lift out as boat was sinking. Because of water ingress port engine wasn't stopping so he had to go into engine bay to manually switch it off.
Skipper (understandably) was very shaken.
Anyone got have photos of the incident or damage?
He'd been working at Hamble Point on Monday.
He indicated that Jet Ski was heading across MOBO's bow. Rider jumped (or fell) off. MOBO swerved to avoid rider and hit the jet ski.
Major damage to one of the mobo's drives and water coming into engine bay so had to have an emergency lift out as boat was sinking. Because of water ingress port engine wasn't stopping so he had to go into engine bay to manually switch it off.
Skipper (understandably) was very shaken.
Anyone got have photos of the incident or damage?
jrudge
Well-Known Member
Let’s hope jet skier has insurance.
Given how it was apparently been driven the rider does not seem that responsible so probably not. As I said in an earlier post sometimes they get too close
Given how it was apparently been driven the rider does not seem that responsible so probably not. As I said in an earlier post sometimes they get too close
Portofino
Well-Known Member
Your “ require “
Ps read the para before and take both paras together .
For ease here they BOTH are ——
————————/————————-/——————
[“So it’s possible if designed right with the CoG as close to the centre of lift ( see the dark chevron in pic 1 ) that the AoA will NOT noticeable change in the planning speed range .
More likely if true mid engined , less likely the engines are shifted back .
Any extra Kg ,s or any additional kgs like a big tender on the bathing platform will exacerbate stern sinking .
This creates a grater wetter area and more drag , less speed .
It’s true you can have a hull which require 0 tab to plane , and 0 tab throughout planning speeds .
Only tab needed down in a head sea to get more parting from the front finer sections and minus tab ,ie up from the horizontal in a following sea ( going fast ) to get the bow up to minimise broaching .
Other than that 0 all the time .] “
————————/—————————/———————
Don,t know where you get / got quote you “AoA remains constant “ that’s not what I said or inferred and apologies to everyone if that’s what you took from the last two para s ?
I draw your attention to the first line and part of the second line of the para above where I said —-
“ that the AoA will NOT noticeable change “
This means it will change but not a lot .
it does not mean “ constant “
Could be reworded to hardly change , or minor change ,or insignificant change etc
Remember we are talking in the planning range say 18 knots to what ever .
We not talking getting over the hump or poppingup etc .
In another life ( attempting to get back on thread ) I n the early 90 ,s I did developement testing for Seadoo .
In those days sit on jet skis were an emerging market and the factory had a sponsored works racing team .
We used to enter various “ raids “ long off shore races in the sea ,of 100 miles + ,eg Marseille to St Trop —- er and back !
Sea keeping determined the winner basically .Not Hp which equates to flat lake speed .
This is not what they were initially designed for back then - which was flat lakes .
Unlike a boat we could angle the nozzle down thereby directly lifting the stern and increasing the finer bow contact ,but at the expense of speed drag ( inc in wetted area + nozzle drag ) and loosing some fwd thrust vector .
Over 100 miles every fraction of a knot counts .
We the moved to hull form and studied this book
Naval Architecture of Planing Hulls by Lindsay Lord .
We were up against Kawasaki ,Yamaha and Polaris works / Factory teams .
One evening we actually glassed up a deeper V with lifting stakes all the way to the transom of the wetted runing area of my ski . Folllowing my instructions - so hopefully you can see where my fascination with hull form comes from :encouragement:
And apologies in a nerdy trains spotter way , why I allways seem to look at threads though those specs .
Forecast was F4 —- I wiped the Floor with the oppersition .
We had a total of 4 hulls runing —-
Some guys suffered compressed vertebrae disks others sore knees , i was mostly OK .
They were quite physical events hard on the riders and kit .
From then on Seadoo went on to redesign the hull form of its products for the Sea and the rest as they say is history!
Let’s leave the Champagne for a mo MapishM,
Instead is it possible I come aboard your boat armed with a cordless drill and a few wine bottle corks .
Allow me to drill two holes in the mid lines at the dock through the hull .
First in the Black area on diagram 1 and the other in the rear white area say between the shafts .
Measure the height of the water jet as it 9isses in of both holes .
Assume your bilge pumps work k before hand .
Then start the engines
As soon as you turn the props at D speed while manoeuvring our ot the marina the rear water spout will shorten or may be disappear ? Front one hardly move .
When planning the rear will become a vac and actually suck out all the bilge water , your bilge pumps will turn off .
Such is the negative pressure at the stern area .
The front one will spurt higher - such is the lifting force .
Saves you the trouble of reading Lindsay Lords book , the chapter on lift .——
- remember planing hulls only ps .Google the guy .
@ school we all know what Newton is to physics or Darwin to evolution,
But who did “ planing hulls “ —— ? :encouragement:
I just found my old copy clearing out some stuff - nowts changed .
@ Jrudge - most places need to sight insurance at the launch point .
I think I had 3 p of £3M back in the early 90,s and used to let the capitaneries sight and photo copy - back then
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MapisM
Well-Known Member
Intriguing offer, but I must decline it 'cause my boat is still on the hard.
Otoh, I'll tell you what: I'm happy to trust the result of your suggested empirical test even without witnessing it.
Just go ahead with your own boat and report back here, possibly with some videos.
I'm sure that'll make for an epic thread indeed! :encouragement:
jfm
Well-Known Member
You don't need to drill a hole. Just remove hose from a seacock in roughly the right place. One without a scoop. Or if you have fw flusher points on your seacocks (qv, 
) just open those. I'll do exactly that and report back on this in a few weeks . I have an airco inlet sea cock with a flushing point just in front of my engine room door, which I think is the correct location Porto (?)
) just open those. I'll do exactly that and report back on this in a few weeks . I have an airco inlet sea cock with a flushing point just in front of my engine room door, which I think is the correct location Porto (?)
Portofino
Well-Known Member
You don't need to drill a hole. Just remove hose from a seacock in roughly the right place. One without a scoop. Or if you have fw flusher points on your seacocks (qv,
Alternatively see the rear / stern suction effect every day more so on low aspect ratio boats ( long n narrow beam )
Watch this slow speed manoeuvre especially as it turns early on - notice the stern sinking
https://m.youtube.com/watch?v=aHnvI5bQbEQ
Wider beamed boats with greater aspect ratios stern sink less , they create less proportion of suction , more lift .
MapisM
Well-Known Member
Pardon? I can't for the life of me understand what relevant conclusions you can draw from a video showing a speedboat maneuvering at D speed.
Anyway, TBH I have zero wish to restart a debate on which I already agreed to disagree in my boat porn thread.
In fact, I'm happy to leave it there, in terms of technical debate.
But just FYI, since you seem to like YT videos, you might have a look at the following one, which even if related to 2004 was only published a few months ago.
I found it interesting the first time I saw it, also because it shows two speedboat icons like Reggie Fountain and Mike Fiore (RIP) still at the top of their game. A bit long at 20+ mins, but worth watching, imho.
Anyway, I just looked for the bit relevant to this debate which I had in mind, and managed to find it, around 10:30, where Ben Robertson deals with a problem of EXCESSIVE water pressure - go figure...!
This is the direct link, just in case anyone has problems with the embedded version:
https://www.youtube.com/watch?v=jSXARJrwpZw.
Portofino
Well-Known Member
The vid of the Miami Vice Wellcraft Scarab 38 shows stern suction .
It’s exacerbated by narrow beam as you say more so at D speed when they reach max D speed .
Infact at .50 secs when it starts to lift ( max lift from the shaded V area on the pic I already posted ^^ ) the whole thing starts to early plane
You can fit pressure sensors which what Lindsay Lord did on models in a tank and real hulls ,
Drill holes or open seacock s ( JFMs suggestion if more / less in the correct place ) - all a bit of a impractical phaff ,
Or —- find a vid —— hey presto to illustrate.
Your vid above is interesting in some ways ,
It’s pancake flat river running hardly a sea F 4 ?
To me they talking about the engine cooling water flow pressure , which I presume ( happy to be corrected ? ) like any other out drive comes from the leg .Otherwise the leg oil will boil .
There may be additional entry being such is the size of the blocks .
Interestingly they are limited ultimately by the weight distribution, too much lift too far Fwds or is that stern too low ?
AoA is crucial for min drag .
At those speeds the resistance is all abour reducing the wetted area ,hence the stepped hull to intro air to reduce the WA
I suspect the main lift comes from the hydroplanes on the leg , they early on discuss a warping / bending while standing at the back looking at the legs .
Interesting how they use a straight ruler to test the hull alignment.
Water is 800 x more dense than air and at those speeds ( pancake lake speeds every mm means a lot .
Hence shave a bit off under the mid section ,or recontour more like to lower the bow a fraction .
It’s actually a fly over boat deliberately so .
With regards to seaworthiness. ( which this isn,t ) the planing hull is designed in order that the bow bottom hardly comes out of water, its vertical motion amplitudes becomes small in waves. And there is little possibility of ‘fly over’ phenomenon. Therefore, if the real every day hull form often operates in rough water, the hull should be designed in order that the bow comes out of the waves as little as possible.
That boat is at the opposite end of the spectrum.
Ultra Speed and seaworthiness are antagonistic
As said earlier above in one of my posts with the jet skis nozzle , like out drives you can trim them .
At the risk of increasing drag at the higher speed ranges .
Note no flaps as well like a jet ski .
Deadrise looked poor too .
This because it’s just a speed machine for pancake flat rivers / lakes .Its got some but it’s designed to lift right out by the legs not to bash down waves .
It’s exacerbated by narrow beam as you say more so at D speed when they reach max D speed .
Infact at .50 secs when it starts to lift ( max lift from the shaded V area on the pic I already posted ^^ ) the whole thing starts to early plane
You can fit pressure sensors which what Lindsay Lord did on models in a tank and real hulls ,
Drill holes or open seacock s ( JFMs suggestion if more / less in the correct place ) - all a bit of a impractical phaff ,
Or —- find a vid —— hey presto to illustrate.
Your vid above is interesting in some ways ,
It’s pancake flat river running hardly a sea F 4 ?
To me they talking about the engine cooling water flow pressure , which I presume ( happy to be corrected ? ) like any other out drive comes from the leg .Otherwise the leg oil will boil .
There may be additional entry being such is the size of the blocks .
Interestingly they are limited ultimately by the weight distribution, too much lift too far Fwds or is that stern too low ?
AoA is crucial for min drag .
At those speeds the resistance is all abour reducing the wetted area ,hence the stepped hull to intro air to reduce the WA
I suspect the main lift comes from the hydroplanes on the leg , they early on discuss a warping / bending while standing at the back looking at the legs .
Interesting how they use a straight ruler to test the hull alignment.
Water is 800 x more dense than air and at those speeds ( pancake lake speeds
every mm means a lot .Hence shave a bit off under the mid section ,or recontour more like to lower the bow a fraction .
It’s actually a fly over boat deliberately so .
With regards to seaworthiness. ( which this isn,t ) the planing hull is designed in order that the bow bottom hardly comes out of water, its vertical motion amplitudes becomes small in waves. And there is little possibility of ‘fly over’ phenomenon. Therefore, if the real every day hull form often operates in rough water, the hull should be designed in order that the bow comes out of the waves as little as possible.
That boat is at the opposite end of the spectrum.
Ultra Speed and seaworthiness are antagonistic
As said earlier above in one of my posts with the jet skis nozzle , like out drives you can trim them .
At the risk of increasing drag at the higher speed ranges .
Note no flaps as well like a jet ski .
Deadrise looked poor too .
This because it’s just a speed machine for pancake flat rivers / lakes .Its got some but it’s designed to lift right out by the legs not to bash down waves .
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MapisM
Well-Known Member
Well, obviously we must, yet again, agree to disagree - completely!
What you are saying is certainly true of drag boat racing, but the boat in the previous video is a full flagged offshore racing boat.
And as I believe to have already said in the other thread, for seagoing boats, speed and seaworthiness are just the two sides of the very same coin.
If you don't mind me asking, have you ever actually tried a Fountain or similar boat?
The record breaking one in the previous video (albeit specifically tuned just for max speed, in that occasion) is based on their epic 42' hull, a machine akin to the FB patrol boat I posted in the other thread.
Both of which can eat Itamas and the likes for breakfast in ANY sea conditions.
Just check out the other video below, taken in SoF, in white foam sea conditions.
Among other boats, the blue Fountain has essentially the same hull as the boat in the previous video.
There's absolutely no way to keep going at those speeds, unless you've got a seaworthy and extremely stable hull.
https://www.youtube.com/watch?v=qG2SOxZ-6zg.
PS: nope, in these boats the cooling water pickup ain't in the leg. It's in fact the bit pointed by Ben Robertson in the previous video.
And those surface outdrives are based on drive sump. But we are already more than enough o/t, I reckon...
If you wish to delve into that technology, the web is your oyster.
Just collect all you already know on outdrives, and forget it altogether!
Portofino
Well-Known Member
They are bouncing about ( excess vertical acceleration) all over the place , guys knackered after only 11 laps !
It’s in a sheltered bay too **** reason here below
Skimming over not parting , for as said obvious reasons of drag reduction .
This thread point ( sorry for the TD folks ) was about stern suction and the uneven distribution of lift on a planning hull .
By “Ultra “ I was thinking around 140 mph + btw .
But the expression “speed and seaworthiness “ lets take out the ultra and insert high speed are antagonist, because going air bourne means you come down too - up down ,up down , up down .
Other thread the AMG Cigarrette 50 I disputed the ride at speed given the deadrise is more / less the same as the alternative s .- gave a pretty detailed explanation revolving around low kg,s and lower planing forces narrow beams leading to more inclination to get air under it leading to increased vertical acceleration which is there in every vid for all to see .
As far a max speed is concerned , that’s not disputed it’s the comfort that’s compromised
I mean the pic of the Guardia Finanza FB boat gonna come down with a bang a fast bang mind agreed ,ideally it should not be in a fly over situation for comfort and safety.
As said I have raced jetskis - think of them as mini extreme mono hulls , had a few spills from airborne situations or sudden turns or both at speed ,over 40 knots hitting the sea is like concrete,I’ve been knocked unconscious a few times .
Saved by the impact vest .So with a L of less than 2M and approaching 100 Hp ( early 90 ,s ) we were hitting 70 knots where the sea state permitted- pancake flat .
Back injuries common .Busted discs . - that’s all see below
***https://en.m.wikipedia.org/wiki/Stefano_Casiraghi
It’s in a sheltered bay too **** reason here below
Skimming over not parting , for as said obvious reasons of drag reduction .
This thread point ( sorry for the TD folks ) was about stern suction and the uneven distribution of lift on a planning hull .
By “Ultra “ I was thinking around 140 mph + btw .
But the expression “speed and seaworthiness “ lets take out the ultra and insert high speed are antagonist, because going air bourne means you come down too - up down ,up down , up down .
Other thread the AMG Cigarrette 50 I disputed the ride at speed given the deadrise is more / less the same as the alternative s .- gave a pretty detailed explanation revolving around low kg,s and lower planing forces narrow beams leading to more inclination to get air under it leading to increased vertical acceleration which is there in every vid for all to see .
As far a max speed is concerned , that’s not disputed it’s the comfort that’s compromised
I mean the pic of the Guardia Finanza FB boat gonna come down with a bang a fast bang mind agreed ,ideally it should not be in a fly over situation for comfort and safety.
As said I have raced jetskis - think of them as mini extreme mono hulls , had a few spills from airborne situations or sudden turns or both at speed ,over 40 knots hitting the sea is like concrete,I’ve been knocked unconscious a few times .
Saved by the impact vest .So with a L of less than 2M and approaching 100 Hp ( early 90 ,s ) we were hitting 70 knots where the sea state permitted- pancake flat .
Back injuries common .Busted discs . - that’s all see below
***https://en.m.wikipedia.org/wiki/Stefano_Casiraghi
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MapisM
Well-Known Member
And now, what on earth has the tragic death of an old uni colleague of mine to see with this debate? :ambivalence:
PF, it strikes me that your reasoning are strictly theoretical.
The only experience you insist to mention with jetskis is as comparable with a FB long range/all weather patrol boat as my 2.80m dinghy is with my 17m DP.
Interestingly, the only other reply you got from someone else who mentions to have actually tried racing boats is the one from Den100 in the boat porn thread:
"That’s rubbish they’re really good in the rough, have raced a few in terrible conditions."
See, of course that FB boat would "come down with a bang" after taking off at 70+ kts. Any boat would.
The difference between those boats and sport(ish) boats like yours is NOT that those boats bang while your doesn't.
The true difference is that those boats bang and keep going, while yours (and mine obviously, as well as anyone else's boat I can think of here in the asylum), in the same conditions, would bang and fall apart.
It's that simple.
But if you're not willing to come to terms with this well known fact, well, I'm not going to lose any sleep over it.
Did I already say that I'm happy to agree to disagree? I really am, no worries! :encouragement:
PF, it strikes me that your reasoning are strictly theoretical.
The only experience you insist to mention with jetskis is as comparable with a FB long range/all weather patrol boat as my 2.80m dinghy is with my 17m DP.
Interestingly, the only other reply you got from someone else who mentions to have actually tried racing boats is the one from Den100 in the boat porn thread:
"That’s rubbish they’re really good in the rough, have raced a few in terrible conditions."
See, of course that FB boat would "come down with a bang" after taking off at 70+ kts. Any boat would.
The difference between those boats and sport(ish) boats like yours is NOT that those boats bang while your doesn't.
The true difference is that those boats bang and keep going, while yours (and mine obviously, as well as anyone else's boat I can think of here in the asylum), in the same conditions, would bang and fall apart.
It's that simple.
But if you're not willing to come to terms with this well known fact, well, I'm not going to lose any sleep over it.
Did I already say that I'm happy to agree to disagree? I really am, no worries! :encouragement:
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