Any Jet Boat experts on the forum ?

Here's pic of boat I acquired recently. Has Holden V6 and single stage unit Cavitates when you boot it off the mark
Also takes honks to get up but once up its awesome I wonder if too much weight in rear as nose loves bein up in the air
Thinking relocate batt plus fuel tank to front plus some fixed trim tabs

Anyone have any other ideas or experience all new to me it's real good on gas and has no vices except fast planing speed and long time to get it up there and get the nose down it comes off the plane real quick as well
I reckon mtr should have been nearer to the front but can't change that

Bugger can't upload pic here's a link to some

http://www.nzhuntingandshooting.co.n...jet-boat-4468/

I'm not a jet boat expert but swap the Holden for a Ford :D

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Originally Posted by Toby

I'm not a jet boat expert but swap the Holden for a Ford :D

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Right on to it

Then it won't go round corners and I'll have the Ford owners tendency to want to stab people all the time

Sounds like wear ring in jet unit worn or impellers damaged.
Get someone who knows what they are looking at to look at the pump .

Sent from my GT-S5360T using Tapatalk 2

I'm no expert by any means, but check intake grill under boat may have stones or something jammed in grill if so use screwdriver to spread bars stones will drop out if OK check impellors as vietnamcam suggests.

First thing to check is that the grill is clear of stones, then shine a torch up the nozzle and check the impeller clearance to the wear ring, the tips (trailing edges) may need building up.

Looking at your photos it looks like your boat is a J31. These were a Marlborough Marine Dart hull that were usually out board hulls but some were used by Hamiltons as jetboats.
These hulls are deep v and are around 20 degrees so are more suited to deeper water than shallow water.
Because they are a deeper v they will need a higher speed to plane and because they are a short hull as well are sensetive to weigh/load.
The Holden 3.8 should be more than enough power but as it looks like a colorado single stage you are at or over the top end of H.P. for this unit.
I am guessing that the previous power unit was matched to the unit and now that the 3.8 has been installed the extra power combined with a worn unit is causing the problems that you are experiencing.
Idealy a Holden 3.8 would have a 2 stage 7.5 inch hamilton unit behind it to efficiently use the available power but you could get away with a single stage providing you got the correct impellor and nossle to suit and the rest of the unit is in good order.
You could get the bow down by shifting weight forward or pointing the nossle down further but watch out for tendency to bow steer.
Also check the bottom with a strait edge on a fore and aft plane to make sure that previous repairs have not altered the integrity of the planing area.

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Originally Posted by Happy

Right on to it

Then it won't go round corners and I'll have the Ford owners tendency to want to stab people all the time

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Hahahaha :D

Good luck with the boat, Happy. I didn't realise that you could really get jet boats with that shaped hull.

Hi Happy where in the Waikato are you??
I have a good mate in Taupo that is a jet boat freak and is pretty clued up on them. Him and I are in the Jetsprint Circuit for this season
I can line you up with him if you want but you may have to drag it to Taupo for a day. our first race for the season was last week.
Flick me a PM and i will see what i can sort out.

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Originally Posted by Twoshotkill

Hi Happy where in the Waikato are you??
I have a good mate in Taupo that is a jet boat freak and is pretty clued up on them. Him and I are in the Jetsprint Circuit for this season
I can line you up with him if you want but you may have to drag it to Taupo for a day. our first race for the season was last week.
Flick me a PM and i will see what i can sort out.

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Are you able to post up any videos of your races twoshot?

Pics are the best i can do for now.... some idiot put me in charge of the GoPro camera and we only got one race filmed (plus 25 mins after the race) then the batery went flat.
It is on a laptop in Taupo and i cant get a copy for another couple of weeks and its too big to send. I will put it on here when i get it!Attachment 5890Attachment 5891Attachment 5892Attachment 5893Attachment 5894

Attachment 5895Attachment 5896

That boat is wicked, If death himself had a boat that would be it.

Have removed steering nozzle plus the short fixed nozzle. Steering nozzle has T3 Embossed on it. When you use a torch and look up into the unit the impeller you can see is mint as. There are no bits missing on the edges and to me it's near impossible to spot the clearance between housing and tips and there are no rubbing marks at all either It's Colorado exp 30 single stage unit

Any point talking to the manufacturer in CHCh to see if there is an impeller to suit the current horsepower but then how hard to remove the unit and get it fitted


This is the exact rear parts it has

http://www.trademe.co.nz/motors/boat...-548738795.htm

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Originally Posted by Toby

That boat is wicked, If death himself had a boat that would be it.

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Oh you wouldn't suggest that they put a Ford engine in it to make it go better then. .??

I purposely kept about 70% weight aft in my shallow water jetboat so as to haul camp and later, a quartered moose. However, mine is a flat bottom, tunnel hulled aluminum river boat set up to run in 3" of water with a load; otherwise it draws 12" which isn't bad for what it does. I can't say I've ever had any experience with a V bowed jet boat. How's the steerageway?

ok. I work for HamiltonJet and recently helped a friend rebuild a single stage Colorado with a Ford V6. Forget what brand is spinning the jet.

Your basic problem will be that the single stage Colorado is only good enough for about 100bhp. Even the coarsest single impellor is only capable of running without a lot of cavitation up to 130bhp. Here are some links to the user manual.

http://www.hamjet.co.nz/includes/fil...s%20Manual.pdf

http://www.hamjet.co.nz/includes/fil...s%20Manual.pdf

Page 4 in this one gives you impellor info versus bhp.

http://www.hamjet.co.nz/includes/fil...al%20Guide.pdf


It cavitates simply because you're spinning the impellor too quick to push water and the boat. The impellor is digging a hole in the water - it isn't pushing it. A bit like having 500bhp with the wrong differential and 10inch wheels on a car. Some options - make the jet a multiple stage, try a coarser impellor, change the engine to less BHP or just don't jump on the gas so much and let it take time to get on the plane.

Lightening the boat will change affect the planing speed but won't help with getting on the plane if the impellor doesn't match the bhp.

Plenty of good information over on the nzjetboating forum. nzjetboating.com Web Board. - Index

Jonathan

I'm not 100% convinced the engine is overpowering the impeller.
The old Buick motors arnt what I'd call a powerhouse.
You really need to pull the pump unit and measure the clearances
On the Seapoos I have played with, a wear ring that looks good means night and day between one with the correct clearances.
Most wear will be in the front end so viewing from the rear prob isn't the best indication.

Forgot to ask.
Can you get the engine to overev at full pace?

Not comparing apples with apples but my gpr1300r cavitated from brand new. 165 hp single stage.
New intake grate and a progressive pitch solas impeller and it was like it had another 50 horse and actually got traction for lack of a better word.
The extra suck down and power made it corner like a blade in the water with no slide :thumbup:

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Scottrods teed it i feel.... sounds like 2 things... a is worn impeller and b is you really need more stages... im running same engine on a 17 &19 pitch ss tipped impellers 110mm nozzle and it goes like crazy... 90KMHR goin downstream and straight up on the plane... unit was a 3 stage and wasnt very flash at that as very gutless!!!!

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Originally Posted by baldbob

Scottrods teed it i feel.... sounds like 2 things... a is worn impeller and b is you really need more stages... im running same engine on a 17 &19 pitch ss tipped impellers 110mm nozzle and it goes like crazy... 90KMHR goin downstream and straight up on the plane... unit was a 3 stage and wasnt very flash at that as very gutless!!!!

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Was niddys ship an if built up the impeller n skimmed housing an turned impeller to 'wear it's self in' (very nice fit). A spanners the motor went like fuck in putters car before he crashed it an of put it in the ship. Think it's bit much donk for the unit. The nosel was bored out also to let it flow out easier to

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Originally Posted by Spanners

Forgot to ask.
Can you get the engine to overev at full pace?

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Yes... Just jump on it and it flares up. Main problem is not too much the time it takes to get up but the fact the nose is in the clouds. Drops off the plane quite quick though as well.

Im getting a little tapered spacer built to slighty change the nozzle angle as suggested by a few. Yes I reckon it should have been a multi stage unit. Everyone has said that. Ill try to tilt the nozzle starting
at recommended 7.5 degrees in the hope it ll get the nose down a little. Im not going to remove mtr and jet unit as to much other stuff to do , if this dont work Ill maybe relocate battery to up front then maybe fuel tank
and if still no good I ll have no probs selling it. First jet boat I ve owned so picked a cheapy to start with.. I like the sport so Id just save up and buy a grousie and this learning experience is all good as I wont loose any thing. Actually a two person
reliable jet ski would possibly do same things I want to do and could probably launch it by myself where as this needs two due to river style boat ramp. IE 2 Foot drop into the river off the bank so winch it in and out with the truck.
Plate spacerr being made next week so will post once fitted and trialled.

I doubt changing the nozzle angle will make alot of difference.. to get it on the plane better you need to tilt up but the further you go the more steering you lose!!!

The ass will be boggingdown cos the unit wont have the juice to push it up out of the water... putting weight forward may be the better option over adjusting nozzle angle but it sounds like your trying to make up for lack power here...

Try a coarser impeller!!

First prob is get a two stage unit or diff piched impellor check out nzjetboating.com The home of JBNZ Online another forum of good bastards they will have you sorted in no time at all

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Originally Posted by Happy

Yes... Just jump on it and it flares up. Main problem is not too much the time it takes to get up but the fact the nose is in the clouds. Drops off the plane quite quick though as well.

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I mean when you have built up speed and are hammering along (say on a flat lake).. can you overrev the motor or will it hit a wall and not go any further?

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Originally Posted by baldbob

I doubt changing the nozzle angle will make alot of difference.. to get it on the plane better you need to tilt up but the further you go the more steering you lose!!!

The ass will be boggingdown cos the unit wont have the juice to push it up out of the water... putting weight forward may be the better option over adjusting nozzle angle but it sounds like your trying to make up for lack power here...

Try a coarser impeller!!

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If I do that do you have to remove the whole unit to fit it ?
Which means engine and heaps of other stuff in this case as well ...
Id say the way its all fitted plus being a bastard to work on it would be a painful progress..
I ll get the price of the bits and make a call. Would you go to the special coarse impellor ?
They offer standard, fine and special coarse for reduced revs or high power applications.

The boats worth spending hundreds on but not thousands

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Originally Posted by Spanners

I mean when you have built up speed and are hammering along (say on a flat lake).. can you overrev the motor or will it hit a wall and not go any further?

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I honestly dont know if it d blow up or hit a brick wall never full throttled it for long enough.
I reckon it would hit a brick wall. Its does get to a point where you can feel its not going to go much faster so I usually drive it just below that point.
It seems happy at 45 kMH 3800 RPM and doesnt feel like you are gonna wreck anything.

Thanks all for all your help. Have had an interesting chat with Rakaia Marine. The guy knows his stuff seemingly. Had same issues before. Has sold me a wedge which wont fix cavitation but will lower the nose. He knows the boat actually has one in his yard. Coarse impellor no good. Fine and standard similar. Some mods to an impellor could be made but even then not a winner. Been there done that and he said waste of good money.
The coarse pitch impellor needs more hp then we have he tried one and it reduced max eng rpm to 3200 where it hit a wall and max speed accordingly.
. They also haven t had any used impellors for a while and Ham Jet said haven't been produced for years so good luck. He could mod impellor to suit but siad no promises and its not cheap enough to make it worthwhile.
Told me he has a client exact same problem and they spent heaps before getting a two stage unit which made it a different boat altogeather and used the horsepower brilliantly.
So option looks like fit the degree plate,Feather throttle to get away, use it like it is until sell it or change to two stage pump or repower with lighter 100 to 120 hp motor which may still not work well.
Will fit degree plate he s sold me one for like 1/8 of price to make one so worth a go and repost then.

Sometimes you can extend the jet out the back of the transom to push the extra stage out without changing the engine position.

You said "it's worth spending 100's on, not 1000's" - LOL. It's a BOAT - a hole in the water you pour money into. :)

Interesting that a course impeler dont work and only does 3200 rpm!! What revs does urs do WOT mine does 4800!!!

Impeller pitch is like changing gearing, obviously it is to high for the standard combo(the coarse) but could be ideal if the nozzle has been bored there by reducing pressure Ie you have to pump more to get same pressure.
Interesting you can only get 3 pitches, for the ski there was a almost endless variation of straight and progressive pitch and even variations in the progression from front to back of impeller in the progressives.

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Originally Posted by veitnamcam

Impeller pitch is like changing gearing, obviously it is to high for the standard combo(the coarse) but could be ideal if the nozzle has been bored there by reducing pressure Ie you have to pump more to get same pressure.
Interesting you can only get 3 pitches, for the ski there was a almost endless variation of straight and progressive pitch and even variations in the progression from front to back of impeller in the progressives.

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Umm it's 40 yrs old That's the problem no one thought we d be still using them or they'd last that long There were only three choices back in day dot. It's ok just is what it is

Do you reckon I could enlarge the out hole and it may help Be like porting my old BB Chev heads took hours but got there in the end

No.

Tuiman alluded to the nozzle already being enlarged witch combined with any impeller/wear ring damage or wear is not building enough pressure behind the impeller to load the motor, hence lots of revs no go.

A larger nozzel and more flow will (generalizing here) get you out of the hole quicker providing you are still loading the motor IE using all the available horsepower but drop top speed as max pressure pumped will be lower with an impeller that was optimum pitch beforehand.

From your symptoms this could be a large part of your problem.

Trimming it down (with the wedge) will get you out of the hole quicker and make it turn better with less slide, But once up on the plane it will drop your top speed.

But your main problem is loading the motor, new wear ring and rebuilt or new impeller and perhaps sleeving the nozzle back down.
There are propeller heads out there who can mod/re pitch impellers;)

You need to get it out on flat water and up on the plane give it WOT and see what revs it will pull.

Ok so have the wedge comin. Was gonna fit and try first any way so will trial and full throttle see what happens Record details and post them. Don't forget tho that the supposed guru of these has said don't throw money at as been there done that. Get a two stage trouble is they re expensive and the boats not that great so maybe move on ?

Take note of max rpm under WOT

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Originally Posted by scottrods

a hole in the water you pour money into. :)

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Yep, may as well stand under a cold shower rippin' up hundies... :XD: