Performance Issues

[Madmax]

Hi
I have a 8m grp mfv, it has a Volvo TAMD 63P (370HP) inboard diesel driving what I believe to be a PP jet drive, I don't know the model and don't know how to find out.
The problem is it won't go very fast. At 1800 rpm it can do 7.5 kts, at 2800rpm (max RPM) it will do 8.5 kts, a lot of noise but no speed.
Is there a simple answer to this?
Many thanks to anyone who can help
Nick

[rasorinc]

Is it a displacement hull?

[Madmax]

No its a planning hull, but doesn't seem to want to get on the plane
thanks

[rasorinc]

the first thing I would check out is the impeller and intake on the jet. I am not familiar with that brand. Does it appear to discharge a large volume of water. You have pleanty of power, perhaps the jet is to small.

[Madmax]

It does seem to discharge a large amount of water, and yes the jet does seem rather small, but this was fitted by the manufacturer, BJR Westral

[anthony goodson]

If it is a PP Jet and was correctly spec'd then it will probably be a PP 115 or a PP140 , VOSPOWER took over from PP several years ago and are still selling spares ,just google it for contact details There is almost nothing goes wrong with these jets if they are used intelligently ,Richard Parker was way ahead of other jet manufacturers in his time and made the best jets available ,look for a simple or obvious problem. Blocked inlet, blocked outlet ,weed growth on boat hull ,high impeller tip clearances [ajustable] damaged impeller blades or sucking air round the handhole cover Jets are the simplest of machines they suck water in one end and blow it out the other with a minimum of moving parts .

[Madmax]

Hi, thanks for the replies
The inlet and outlet no not appear to be blocked, the hull is clean.
When I take the inspection hatch off and put my hand in, I can fit my fingers between the impeller tip and the tube, is this the right clearance, how do they adjust? One of the blades has a small chip and a few barnacles can be felt, but i don't think it will cause such a degradation in performance.
How would I find the handhole cover to see if its sucking in air.
Sorry to be a pain, any help is greatly appreciated
thanks
Nick

[anthony goodson]

The handhole cover is the inspection hatch, this is on the suction side of the impeller so just check that the gasket is intact and sealing.or it will draw air rather than water The impeller runs in a stainless steel wear ring which is cone shaped .The tip clearance is adjusted by adding or removing shims around the shaft in front of the impeller,the less shims the smaller the clearance. If you dismantle the jet,remove and replace the impeller without the woodruffe key but with the tailpipe, you will be able to turn the impeller by hand through the inspection hatch and ascertain how many shims are needed ,in practice the clearance should be as small as possible WITHOUT TOUCHING the wear ring, count the shims and replace the key .Impeller blade condition is more critical than propeller blades ,barnacles will cause cavitation/ventilation These instructions apply to most models of PP jets why not post a photo so that we know which model we are dealing with and that it is a PP jet

[Madmax]

Hi
Thanks again here is a picture of the boat, I will go and take some of the jet tomorrow and post them

[anthony goodson]

Hi
Yes looks like a PP jet the PP embossed on the bucket is a bit of a clue. Think it's probably a 140, a succesful fibreglass bodied Jet .Measure the impeller diameter ,if its 14 inches [356mm] then thats what it is.
This model went through several development changes and there were several shaft, nozzle and rear bearing options depending on application If this is a 140 it is the right spec for your boat and should perform well Vospower will almost certainly send you a parts list and exploded diagram which will help you with dissassembly call them on 02392539739 or e-mail vtmpspares@vtplc.com

[Madmax]

Well its been a while now but I had the boat out of the water, after cleaning the hull and putting her back in the water I managed an extra knot but no significant improvement.

Does any one see that the impeller may need replacing, its not very smooth at all, many pits and chips around the outside, are these repairable?

I cannot measure the diameter very well because of the shaft, but it appears to be just under 12 inches.

Any contact info for anyone who could help would be most aprreciated.

Thanks for looking and to anyone who can help.

regards

Nick

[baeckmo]

The diameter you mentioned, is that the dia of the outlet side of the impeller? And, please check the outlet dia of the nozzle as well, because if you have an impeller outlet dia of less than 12 in., it will be a PP100. If so, the nozzle would read 6.0 in (152 mm). As Anthony has already noted, it ought to be a bigger size jet; the PP100 is not a very good match for your boat/engine combination.

Your jet is probably cavitating or ventilating heavily, which means that we have to be quite precise in diagnosing, but there is room for improvements, provided we have correct info.

Any ideas on boat wheight?

Could you produce a pic from below, say midships, looking aft along the center line, so the inlet position and those "vanishing tunnels" are visible? There may be a problem with air trapped in the tunnels beeing sucked sideways into the jet when the jet is demanding increased flow to overcome the hump.

[Madmax]

Hi,

thanks for the quick reply

if you can zoom in in pic 2 you will see the tape measure, i'm not completely sure of all the part names

i've added another pic, which is about the best one, the boat is back in the water now

i am not too sure of the boat weight and would be guessing at around three ton

i did locate a part number which is 1155029, which was somewhere on the bucket - do i assume that the first part 115**** is probably the model number?

thanks again for your help

regards

nick

[anthony goodson]

Good morning Baeckmo ,could also be a PP115 which wouldn't be quite so bad. measure the inlet side of the impeller,this is where the measurement is taken also the standard nozzle on a 115 was 7.5 inches but there were other options.

[anthony goodson]

Your last posting crossed with mine ,if it is a 115 then it was designed to give a planing performance with boats from 2 to 4 tons with engines up to about 300hp, not as good as the 140 I originally thought it might be ,but never the less,should perform ok the two jets look very similar from the bucket end ,just different sizes ,both were GRP.As Baeckmo says more information is now needed

[Madmax]

Hi

very fast responses today, thank you

what would be my next step, to be honest, if i could find somebody locally (Weymouth) I would just pay to have it fixed.

However, nobody around here seems to know much about jetdrives and Vt are taking a long time to answer my emails.

Just to recap for me, what info do I need to give you in order to solve this problem.

many, many thanks again for your help, it is much appreciated

kind regards

Nick

[anthony goodson]

These are the performance charts for the 115 if it is a115, Baeckmo will probably be the best source of advice on your hull but as he says he will need more info In my previous post I mentioned impeller tip clearance and air leaks which are both of paramount importance and apart from debris in the jet which you will have seen ,that is about it for the jet Do consider that jets are very weight sensative and all boats grow in weight the longer we own them as there are more and more possesions that we can't do without and we stow them on board, perhaps your 3tons is a little conservative

[Madmax]

Hi

Considering the condition of the impeller, do you think I should just replace it as this to me seems to be important, or is it possible to get it repaired, if so do you know anybody in the Uk?

thanks once again

kind regards

Nick

[anthony goodson]

I always recommend to people that they remain seated whilst enquiring about the price of a new impeller it's safer that way.I can't say that I know of a specialist in impeller repair, but your local prop repairer should be able to do it. Tip clearances are also very important ,and you are very lucky .as these are adjustable on this jet .Make sure your prop repairer understands that the impeller runs in a cone ,and provide him with the dimensions. Dennis at Poole Propellers always did an excellent job ,but sadly they closed down.

[baeckmo]

Right then, it seems you have a PP 115, which is a bit more promising for you. The impeller (pump rotor, propellor, ....) is looking slightly moth-eaten and is not properly adjusted axially within the conical housing. So it has to come out to see some welding and general refreshing.

But before that, while the boat is in the wet, it would be of great help if you could perform a bollard-pull test. You need a pulling scale, capacity ~1000 kg (and a reliable bollard.....). Measure thrust from 1200 rpm and upwards with 200 rpm intervals. At a certain rpm there is no further thrust increase; there will be full cavitation. Sounds like a shovel of gravel playing havoc in the jet unit, abort the test at this load. In spite of the impeller being in need of repair, this exercise will give me basic input for a check on the jet/engine matching.

Then to the hull; unfortunately the picture from up front is not showing the aft, important part of the hull with the jet inlet. Maybe the boatbuilder could be identified and persuaded to supply some transverse stations before you drydock again???

With a "normal" vee bottom and a weight of 4 tonnes, you should have a speed close to 30 knots with everything ok. My experience with the VP 63 series has shown this engine to produce power around the lower tolerance limit (-5%), rather than the opposite.

[Madmax]

Thanks anthony and baeckmo, i'll be back

[Highlanderwj]

Just for information.
I have been running a twin Hamilton jet boat for 10 years.
Anything that changes the flow will reduce the thrust to almost zero.
A few times, a small piece of line wrapped around the shaft infront of the impeller. Many times some seaweed would find its way into the jet.
Vibration and slow speed are the result. Judging by the photo, you need a good freshening up. Barnicles or a chip or tip clearance too big will cause a problem. You have all three!
I have my jets serviced every year and love the performance and manuverability.

[baeckmo]

Nick, I saw a hull very similar to yours in Cork a week ago. Had a look at it when it sat dry. It confirmed my thoughts that your trouble comes from excessive amounts of aeration. These designs have an inverted "V" where the main hull connects to the sponsons, and here you get a intense mixing of air/water. This foam reduces the speed of pressure waves in the mix, as compared to pure water, which in turn will reduce the slamming pressures on the hull.

Problem is just to keep the mix away from the jet inlet, as it will spread and follow the bottom. There are two ways; either longitudinal side fences each side of the inlet, or letting the inlet have a "collar", so that it will pick clean water.

I'm curious regarding your results, so pls "report" ......

[lyinhell]

A prime mover connected to the jet drive can be coupled either directly, or a marine gear can be used to facilitate clutching in/out.
If you are using a marine gear, check your reduction ratio.
My 27' aluminum hull is driven by aYanmar 240 hp, twin disc 1.1:1 into a Nomera N800
Top speed 25knot @3300 rpm nozzle diameter reduced to 7.25" from 8.0"

[Madmax]

Hi Baeckmo, thanks for not forgetting me.

I am totally lost at this point, I must admit that I am totally not technically minded. but here is an update:

I have not been able to locate anyone who can do a bollard pull test, or anyone who could lend me the scales to do it myself.

I have found a chap who specilises in propellors and impellors and deals with VT, he has looked at the photo's and believes that the impellor is not repaiarable because it is too badly worn, he is prepared to take a look when I get it off, he has stated that he can 'cast' a new one if it's not repairable.

I also found a chap who can take it off and put it back on again, but I don't exactly trust him because he doesn't come across as all that knowledgable.

Another chap has said that I should replace the liner aswell?

VT have moved offices and are taking a long time to get me any diagrams, parts lists etc.

I plan to take more photo's when I get her out of the water again, but of course I don't want to do this until I know exactly what I am doing. For example can I take off the impellor easily and more importantly will it just go back on again or does it get even more technical? ie the liner and tip clearances etc?

How do I fit 'longtidunal side fences' or a 'collar'?

Sorry if I seem a doughnut but I just enjoy fishing.

Thanks again everyone for your help

regards

Nick

[baeckmo]

Nice to hear you are still with us, Nick! Where in the UK can you be found? Fiddling with the mechanical parts of the PP jets is fairly straightforward, maybe Anthony could give a hint on a decent mechanic? Do you have an owners manual for the jet?

Impellers may look quite moth-eaten, but are still repairable. It may even be feasible to to have it fixed here; lets come back to that. BTW, did I refer to Mr Brent Voce at VT? He was (is?) involved in the VT jet story, and he is one of those rare characters with excellent knowledge on the product and a nice fellow.

I'll make a few scetches for you on the fences/collar issue later on.

[Madmax]

Hi baeckmo

I am in Weymouth which is on the south coast,

I have spoken to Brent Voce at VT, but they have recently moved offices and they seem to be in turmoil at the moment, I don't have any manuals but should be able to get one from VT once they get organised. He is a very knowledgable person and very pleasant with it, he is hopeful to get the info from deep within the bowels of VT as soon as he has recovered from the move.

regards

Nick

[anthony goodson]

Good afternoon Nick and Baeckmo
I can't recommend anyone on the South coast I'm afraid, but why not have a go yourself, jets are very simple .it's not like rebuilding a gearbox or a leg.Your impeller should be 317 stainless if it's original ,a good prop repairer should be able to rebuild this even if it is a bit knocked about.When you receive your parts diagrams from VT study them carefully you will see how simple this thing is .As regards the wear ring unless this is very badly scored leave it in. Replacing the wear ring on the aluminium models was commonplace because the aluminium {LM6 ] corroded and "grew" under the ring and pushed it out of round,this won't happen on your jet because it has a grp body.
I am sure you will forge a good relationship with VT and you may wish to order spares from them but just be aware that although this jet was designed by a brilliant engineer there is a lot of the"cottage industry "about it and many service parts are available from your local bearing supplier.The front bearing is a standard opposed taper roller the rear bearings are DU bushes by glacier and all the seals are standard sizes If you buy the seals locally change the springs for stainless ones Good luck,keep in touch ps I have just remembered some 115's had a cutlass bearing in the stator not a DU bush

[anthony goodson]

These "fences " are on a cathedral hull similar to yours, you may consider these later when you have rebuilt your jet, Hopefully Baeckmo will be able to give you some dimensions suitable for your hull