engine for nelson 34?

[Latestarter1]

was thinking more of marinising a turbo 4236 than trying to turbochage mine. But think the turbo is in the way so no space for the heat exchanger. Is probably a no go. Think the 4236 is 85hp (67kw) by memory, not 100% sure. Cheers

As others pointed out Perkins base hardware changes to accept turbocharging.

You would have some major hurdles. The 4.236T out of JCB 3CX was similar power to your own motor, about 85 Hp, turbo low blow set up and was used more to change shape of the torque curve for excavator duty cycle and not for significantly greater power.

You will struggle to find suitable turbocharger match, and will it fit on your marine exhaust manifold.

Your cooling system cannot handle any more tha 100 hp in Northern European sea water LAT.

You would need a charge air cooler. Changes feaseable but never practical.

20/30 extra horsepower will do squat all for you. You will need minimum of 210 hp to make any difference.

If you can accomodate extra 5 inches installed length Cummins 6BT would go, and if you have BW72CR box that would go straight on the back.

If you cannot accept extra 5 inches of length only real option is a Yanmar 4LHA 240, however near impossible to nail your current box on the back of the Yanmar and reduction ratio would be all to heck anyway.

 

[supersparky]

So, you extensively modified your boat to do the French canals, eventually got over to France, but did not go into the canals, you then came back and have decided to change your plans/ boat again, might be a good idea to sleep on it for a little while before you make your next move.

Hi,
I have just bought a Nelson34 MkI with aft cabin, looks like a Tyler moulding, and is in need of heavy TLC. Fitted with Perkins 6.354 and 1:1 box from Self Changing Gears of Coventry. The prop is much too big (Probably matches the 145hp turbo) so I only get a max 1600rpm which computes to about 80-85hp instead of the 110shp at 2400rpm. At fullpower I get around 10 kts with the wake pattern just pulling away from the transom.
The boat is 32ft on the waterline. The square root of 32 is approx 5.5. Multiply that by 1.4 to give the "Hull Speed" in Knots, i.e. about 7.7 Kts. There is little point in going much faster through the water unless you are in the supertax bracket. I think that if you have an big well matched prop less than 60shp is needed to achieve hull speed in reasonably calm water with a clean hull and not too many draggy bits like anodes, rope-cutters and bilge keels. But then I am new to this type of craft.
What is your Max rpm? and what is your cruising rpm? Your u-tube video seemed to have quite low rpm on the engine. I would expect your 4.236 to give about 8knots and if you do not reach 7.5 knots at 2250rpm (Max Continous) then something is wrong.
Have you a photo of your propellor?
My middle name is Scrooge (I am proud that I was once accused of being a Scottish Jew) I do not cruise above hull speed without good reason and will use the Tides to slingshot the boat around the Solent, the Channel Isles and Chenal du Four. Yes a 19 hr passage is a bit long but with properly organised watches and a stop-off for duty free fuel in St.Peter Port, getting there is so much fun. Regards

 

[Mulroog K]

Hi, Just thought I would add some info to the thread. Wondered where all the hits on my utube post came from... guess now I know !

I have just completed a re-engine of a nelson 34 aft cabin which previously had a single 6354 (110-120hp) runnning a 2:1 SCG box and a 21x19 3 blade prop. Weight aprox 5000kg. This gave 15kts max at 2400rpm, however in reality you could not really put up with more than 10-11kts due to general mechanical sympathy, not to mention noise.

This is a problem for this hull as it is a narrow beam boat running only a little over full displacement speed... ie rolls considerably. At its max of 15kts it is begining to get the nose up and runs far better, but as above you just cant keep it at this speed.

After lots of research, debate, and hesitation the decision was made for a transplant and a Nanni 320hp 6cyl was chosen. This is the Toyota landcruiser unit and almost identical to the Yanmar equivalent. The target horsepower was much less however this engine is now only available in the 320 as it is almost end of life, and it was the only engine that had any hope of fitting in the narrow engine bay. The first choice was the perkins 225 but the odd placement of the raw water pump rulled it out.

Coupled with a 750C 2:1 inline box (300mm shorter than the SCG!) and a repitch of the existing prop to 21x23, a new duplex shaft on the existing 1.5" dia and a whole lot of work later including major bracing of the existing engine beds it was in and time for trials.

At 3600rpm exactly WOT the boat achieved a whisker over 24kts and a comfortable cruise of 20kts. After a few hours splashing about it is clear that this hull is only at its best north of 17kts, it becomes very stable can take some major sea without fuss. This is truely what the semi displacement hull is designed for.

If you are planning for displacement only, I would suggest you only need in the region of 100hp or so, however if you want some pace, you are going to need some hp. In hindsight I am glad we did not install around the 200-225hp mark as it would likely not have achieved the target of 18kt cruise. Possibly a max of 18 or so.

On a 5hr round trip most of it at 17-18kts plus the usual slow running it burned 100L. so as a rule of thumb you could take 25L/hr at 18-20 kts cruise with this configuration.

Thanks to Brian at AR Peachment and thanks to Paul at Clements Marine for some superbly accurate calculations and prop sizing!

Hope this is of interest and some help. plenty of more info to anyone in need of it.

SuperSparky, give me your hull number and I will tell you when and where it was built. It should be four digits and be on the front bulkhead.

 

[boatmike]

I have just gone through the same thought process. Having reached the age where ocean cruising is too much for me (and particularly her indoors) I have sold my 37ft sailing cat and bought an Aquastar 33 with twin Volvo TAMD41a in. That's 400HP. My thinking was based on wanting to travel easily and safely (and sometimes quickly) in the channel and med but leisurely through the canals too. I looked at Nelsons because I spent a lot of my working life building them. Mostly I was involved with 44s as pilot boats, police boats etc etc but most of the smaller ones were harbour launches or pinnaces for RN vessels and in this guise didn't have to go fast so about 100-120HP was sufficient. The hulls are similar in design to the larger ones though so quite capable of semi-displacement speeds of 20 knots and more with twin engines of about 200HP each but with only 10ft 6 in beam do roll somewhat..... My thinking was that the Aqua-star 33was very similar but beamier at 11ft 6in and with twin engines I could give me 20knots when I needed it but would cruise nicely at 7-8 knots and be much more economical. I could also navigate canals at a tickover... However it's a compromise. If your smaller engine is reliable and gets you there what's your hurry? It will be very economical in the canals and you won't have to worry about sooting up your turbos! If I was to be spending most of my life on the canals I would stick to a small engine. On the other hand if you are only transiting the canals to get to the med like me you can fit larger but dont forget to up your fuel tanks. I carry 900 litres.....

 

[supersparky]

Hi Mulroog K,
Thank you for the info. "Minnihaha's" MOD. No is 6757 34FT MA20(the 2 is defaced and could be another character) The boat came with only wheelhouse windows, and the current small smoked plastic windows were fitted in the mid 1990's by the previous owner (They now leak). Proper windows on the way.
The machinery can stay as it is for a year or so, while we tart up the aft cabin. Currently lowering the floor to give 6'2" under the 1" deck beams and making quarter berths into the aft peak and the Stbd side engineroom.
Have lowered the tickover for the rivers and locks. 400rpm gives 3kts but it pulls up sharply enough in reverse but with a strong kick to the right. There is substantial clutch drag in neutral as a shaft brake was not fitted on this box. This makes for an interesting time in the locks!
I understand your comments about 240hp plus to give a comfortable ride, anything less and it feels underpowered. There is not that much room for a propellor to take that much power and you had to beef things up a bit to take the thrust and torque. Well done.

 

[Latestarter1]

Hi, Just thought I would add some info to the thread. Wondered where all the hits on my utube post came from... guess now I know !

I have just completed a re-engine of a nelson 34 aft cabin which previously had a single 6354 (110-120hp) runnning a 2:1 SCG box and a 21x19 3 blade prop. Weight aprox 5000kg. This gave 15kts max at 2400rpm, however in reality you could not really put up with more than 10-11kts due to general mechanical sympathy, not to mention noise.

This is a problem for this hull as it is a narrow beam boat running only a little over full displacement speed... ie rolls considerably. At its max of 15kts it is begining to get the nose up and runs far better, but as above you just cant keep it at this speed.

After lots of research, debate, and hesitation the decision was made for a transplant and a Nanni 320hp 6cyl was chosen. This is the Toyota landcruiser unit and almost identical to the Yanmar equivalent. The target horsepower was much less however this engine is now only available in the 320 as it is almost end of life, and it was the only engine that had any hope of fitting in the narrow engine bay. The first choice was the perkins 225 but the odd placement of the raw water pump rulled it out.

Coupled with a 750C 2:1 inline box (300mm shorter than the SCG!) and a repitch of the existing prop to 21x23, a new duplex shaft on the existing 1.5" dia and a whole lot of work later including major bracing of the existing engine beds it was in and time for trials.

At 3600rpm exactly WOT the boat achieved a whisker over 24kts and a comfortable cruise of 20kts. After a few hours splashing about it is clear that this hull is only at its best north of 17kts, it becomes very stable can take some major sea without fuss. This is truely what the semi displacement hull is designed for.

If you are planning for displacement only, I would suggest you only need in the region of 100hp or so, however if you want some pace, you are going to need some hp. In hindsight I am glad we did not install around the 200-225hp mark as it would likely not have achieved the target of 18kt cruise. Possibly a max of 18 or so.

On a 5hr round trip most of it at 17-18kts plus the usual slow running it burned 100L. so as a rule of thumb you could take 25L/hr at 18-20 kts cruise with this configuration.

Thanks to Brian at AR Peachment and thanks to Paul at Clements Marine for some superbly accurate calculations and prop sizing!

Hope this is of interest and some help. plenty of more info to anyone in need of it.

SuperSparky, give me your hull number and I will tell you when and where it was built. It should be four digits and be on the front bulkhead.

Very good call, not sure how research came up with Perkins Sabre 225 as first choice, however as luck would have it you rightly ignored an asthmatic old 190 Hp ground anchor for what is certainly a super base motor. And the results speak for themselves.

In order that you continue to protect your substantial investment I would just lie to make a few observations.

Toyota 1HD-FT is as I mentioned earlier a darn good base motor. Forget all the 320 Hp stuff, ISO 25 C test fuel wishful/marketing stuff, this is a good honest 220 kW, 300 hp (metric) engine which really delivers.

I have no clue why Nanni rate the engine at 3,600 rpm.............Toyota 1HD-FT spec sheet and equivalent Yanmar LY spec sheets both give rated speed as 3,800 rpm?? Do not let anybody try to tell you it is 'tuned' by Nanni, the RCD compliance documentation is based on Toyota 1HD data.

Once you have the answers to the above I am concerned regarding your comment 'At 3600rpm exactly WOT the boat achieved a whisker over 24kts'. Yanmar learned the hard way and issued a 'Judgement Standard' on propping their engines. Yanmar 6LP requires propping in the range 3,950-4,050 and targeted at the higher side of WOT to take account of weeding and to ensure engine is not overloaded when running in this condition.

Paul at Clements is a bugger for trying to outsmart the competition by propping real close to the edge and taking no account of weed growth, take this conjunction with the slightly odd Nanni WOT of 3,600 rpm and the fact you are propped right on the edge of this slightly questionable figure. I know exactly what Paul will say..... 'Do you want an egg whisk or a propeller'. Can we assume when Peachment did sea trials that they checked tacho with strobe and the figure of 3,600 rpm was off the digital tacho? No clue about accuracy of Nanni tacho, however you do need to be aware is how far out it is. One serious nausia with Yanmar tachos is that they tend to over read, adding to potential risk of overloading.

One final thing, took a look at the Nanni data sheet, please please tell me that you do not have the set up with the water filter on the pressure side of the raw water pump, utter madness. If you have this nonsense just rip it out and install a decent quality strainer on the the suction side from say Aqafax, none of the plastic stuff!

Check out the above and you will have performed a super transformation of the Nelson hull which will be problem free. Remember poor old Clifford of Guernsey who posted here, with his repeat engine failures, ensure it does not happen to you.

Good luck

 

[PCUK]

60 litres for 19 hours running? You must have been on tick-over. Expect at least four times that amount with a bigger engine.

 

[Mulroog K]

Latestarter,

Thanks for the comments. Agreed a beautiful engine, pity it is near end of life, high power, light weight, narrow, car like balance and not a circuit board in sight. : )

I did the modifications, install and sea trials myself and did calibrate the tacho with an external optical tacho... it was a long way out. This was because I asked Peachment to ship the older style panel with the engine as it fitted my install better... it so so far out that I had to question the garbox ratio and the prop repitch, but one calibrated all was well.

Water strainer after the pump... really? not in this case.

I am aware that the yanmars are noted for sensitivity to overloading but for me the way I have it makes most sense for my use. Top speed is forum and pub talk, in reality you want a low cruising rpm at the speed you want, in my case about 2900 to 3100, if you look at a typical prop curve at this rpm the power reserves are plenty as born out when you open the throttle giving quick acceleration not sluggish rev building. So yes your point is correct, I am propped to the max, but as I will never run near this, all is well. Another confirting factor is that at cruise I burn 25L/hr aprox, Nanni quote nearly 60L/hr at max, suggesting a very comfortable power reserve at cruise.

BTW.. the only reason for considering the perkins was they are highly discounted, they have there uses, but I would suggest not in a fast low hours pleasure boat.

With regard to Paul, I would not be so hard on him, all I bought from him was a new shaft and he genuinely was the only person who could correctly predict the verified top speed of the existing install, most including perkins were out by 2 -3 kts. Likewise for the new install. plus he gave me a half hour of his time for free not to mention the experience he has and the confidence it gave me to take on the re engine.

I could share some pics of the restoration if anyone is interested, can you load pics on this forum?

SuperSparky,

I have looked up your hull number and turns out our boats are siblings !

Mulroog K is MOD 6755.

Both boaths were built for the MOD by Watercraft marine on the south coast. They are MOD Mk4 and Keith Nelson MKIII (this batch noted for their higher wheelhouse). aparently the lower wheelhouse type were used for the side loading onto the naval ships. They first two digit are the MOD year of ordering and the second two are the hull number in sequence for that year. Typically commissioned a yr to two after.

Any chance your MA20 could be MK3?

I found out my hull was 'PL5' (found under a hundred coats of paint during restoration) and was an MOD police launch based in Devonport Plymouth. I contacted a guy from the small ships organisation as part of the World Ships org who had more info and a pic of her in service, but unfortunately the trail has gone cold.... anyone help?

MK

 

[Latestarter1]

Have no fear of electronic engines. However what you have is 1,000 times better than current crop of new motors, nothing to to with electronics, they are simply chain saw motors in this power node, often with VGT turbochargers completely unsuited to marine duty cycle.

Amazed that Peachment sell engines with no installation review to activate warranty. Sounds like you did the job properly, however not everybody?? Seems a suicidal policy to me when some so called professional builders cannot put a proper exhaust system together, many try to ignore gravity.

How much were Finning CAT quoting for Perkins 225 bobtail, £10K??

If you check out the Nanni/Peachment website shows stainer on pressure side, however this must be stern dive application.

Good luck..

 

[Mulroog K]

After some negotiation 11.5 with box for the perkins if I recall correctly, its been a while so I could be out a little. But it would not fit in any case due to the very awkwardly placed raw water pump.

The exhaust was a challenge, I was terrified of the backpressure values so oversized the exhaust, could not afford to have to redo it a second time. As its a centre engine the run is long and complex. worked out at about 1.3psi at cruise. Not helped by the fact that Nanni mis quote the pressure units as psi instead of bar. Used a 4" run to a ss 4-5" elbow, through a 5" Halyard lift muffler and then a long dropping 5" run to freedom. Worked out well with little or no exhaust noise onboard and a nice low turbo packpressure value.

 

[Mulroog K]

SuperSparky,

You mention u have a 6354 with SCG box, most likely due to age/yard similarity I would expect this was the same setup as mine. Are you sure it is a 1:1 and not a 2:1? mine was 2;1. also I agree the in gear speed was high, 4+ kts I think but would suggest 400rpm is very low... Also there was no clutch drag to speak of, yes the shaft turned but barely..... this would suggest adjustment may be possible and as this is a hydraulic box it may only be a case of adjusting the valve and not the box internals?. FYI I subsequently sold the engine and box but know the box was not used. ie its probably sitting in a shed somewhere and worth very little.

 

[Latestarter1]

After some negotiation 11.5 with box for the perkins if I recall correctly, its been a while so I could be out a little. But it would not fit in any case due to the very awkwardly placed raw water pump.

The exhaust was a challenge, I was terrified of the backpressure values so oversized the exhaust, could not afford to have to redo it a second time. As its a centre engine the run is long and complex. worked out at about 1.3psi at cruise. Not helped by the fact that Nanni mis quote the pressure units as psi instead of bar. Used a 4" run to a ss 4-5" elbow, through a 5" Halyard lift muffler and then a long dropping 5" run to freedom. Worked out well with little or no exhaust noise onboard and a nice low turbo packpressure value.

Thank you for the update on Perkins pricing, sounds like £9.5K bobtail which is peanuts. The latest Perkins Sabre M250 is double that, no wonder they are not selling!

I am afraid you have have terrified me with your exhaust backpressure #'s, perhaps we are talking past each other.

If I remember correctly Yanmar LP back pressure limit is 3 inches of Hg @ 15.5 C. Off the top of my head 1.3 Psi equates to over 3 inches of Hg at CRUISE which is way too high. Backpressure data should be recorded at rated, normally at cruise you should be barely lifting the pin on the gauge. Did you use oil damped or Magnaheilic gauge?

Halliard water lift mufflers are great, streets ahead of usual Vetus junk. Halliard water lift certainly never the cause of backpressure issues. If your numbers are correct I would be concerned regarding the section of 4 inch exhaust run....Once you have slowed down exhaust gases, going to 5 inch does nothing for you. If you want to get the back pressure down you can try diverting some cooling water over the side through a skin fitting. If you have a valve in the line you can spill just enough water to drop back pressure without overheating the exhaust hose.

Let's hope your numbers are a little askew.

Good luck

 

[Mulroog K]

The pressure readings are correct , i too them at the port on the turbo outlet manifold (mixer) with a calibrated Druk DPI 600 pressure meter, so i am confident they are what they say. I was advised that these numbers were good based on checking with Nanni.

I could certainly bleed of some water easily if required.
The 4" section is as per nanni recomendations andis only about 450mm long

Do you think i have been ill advised? What are the consequences of high backpressure?

 

[Latestarter1]

The pressure readings are correct , i too them at the port on the turbo outlet manifold (mixer) with a calibrated Druk DPI 600 pressure meter, so i am confident they are what they say. I was advised that these numbers were good based on checking with Nanni.

I could certainly bleed of some water easily if required.
The 4" section is as per nanni recomendations andis only about 450mm long

Do you think i have been ill advised? What are the consequences of high backpressure?

I have taken the trouble to pull up Yanmar installation guidelines for the 6LP. Latest 2006 back pressure number for is 2000 mm of water which equates to a generous 5.8 inches of Hg, revised up from their older 3 inches of Hg. However this is an ABSOLUTE # and must be measured at rated speed. Over 3 inches at cruise say 3,100 rpm has to indicate some pretty hight #'s at rated speed, as back pressure tends to rise as an exponent of engine speed. It would not surprise me to see over 600 C on the pyro at this test point.

Normal procedure is for selling agent's tech to perform sea trials, check against installation review #'s and then sign off your warranty, are you suggesting Peachment just ship the engine and let the installer get on with the job. Do Nanni not have a proper installation manual??? How the hell do they warrant the product without a baseline..About £13.5K plus installation cost and all dealer wants to do is 'flog em a box'.

Because of builder issues in the US Yanmar re-wrote their guidelines in a very comprehensive format. The 1/8 NPT plug on the riser can be used for checking back pressure as well as EGT.

Excessive back pressure causes poor fuel economy and most critically high exhaust valve temperatures. On the Toyota base engine failure mode is in area of friction weld where stem is connected mushroom, head flips off the valve leading to catostropic failure.

I still have no clue why Nanni have changed the rated speed of the Toyota base engine.

Mulroog sounds like you want to do a proper job and being led by monkeys.

 

[supersparky]

Nelson 34 - Aft cabin version

SuperSparky,

You mention u have a 6354 with SCG box, most likely due to age/yard similarity I would expect this was the same setup as mine. Are you sure it is a 1:1 and not a 2:1? mine was 2;1. also I agree the in gear speed was high, 4+ kts I think but would suggest 400rpm is very low... Also there was no clutch drag to speak of, yes the shaft turned but barely..... this would suggest adjustment may be possible and as this is a hydraulic box it may only be a case of adjusting the valve and not the box internals?. FYI I subsequently sold the engine and box but know the box was not used. ie its probably sitting in a shed somewhere and worth very little.

Hi Mulrook K,
Sorry not to have replied to your post earlier. 'Minnehaha' is now fresh out of drydock, and with the spare prop in place (same as original 4 blade plastic prop but less distorted). Now comes fully onto the plane at 1800rpm instead of only 1600rpm, and with no vibration. GPS still not fixed yet, so no accurate speed indication, but the boat was empty of fuel and water so I guess the prop is still a bit over pitched, but that suits me as we will only cruise at hull speed (7.7kts) or less. The underwater surface is still very rough but I may get a chance to scrape back to the gel coat next year. I will do some engineering to give us an alternator to operate down to 500rpm, ours cuts out below 950rpm which is about hull speed. Our refit will be ongoing over the next few years starting with superstructure paint and then the aft cabin which already has a lowered teak faced plywood floor. Will move the Whitlock steering shafts and gearbox to make another bunk space. Batteries are fine on the 2 solar panels, low energy lights are in, and a 24 to 12v converter is about to be fitted.
Would be nice to see the pictures of your refit, (my e-mail is alexisvilliers@hotmail.co.uk). I have however made a decision, particularly if I re-engine, not to go planing. I know it is a waste of a lovely hull shape, but the pressure is on to burn less fuel.

 

[Bluebelle 3295]

Re-engine Nelson 34

I have just completed a re-engine of a nelson 34 aft cabin which previously had a single 6354 (110-120hp) runnning a 2:1 SCG box and a 21x19 3 blade prop. Weight aprox 5000kg. This gave 15kts max at 2400rpm, however in reality you could not really put up with more than 10-11kts due to general mechanical sympathy, not to mention noise.

This is a problem for this hull as it is a narrow beam boat running only a little over full displacement speed... ie rolls considerably. At its max of 15kts it is begining to get the nose up and runs far better, but as above you just cant keep it at this speed.

After lots of research, debate, and hesitation the decision was made for a transplant and a Nanni 320hp 6cyl was chosen. This is the Toyota landcruiser unit and almost identical to the Yanmar equivalent. The target horsepower was much less however this engine is now only available in the 320 as it is almost end of life, and it was the only engine that had any hope of fitting in the narrow engine bay. The first choice was the perkins 225 but the odd placement of the raw water pump rulled it out.

"Looking for help"

I offer apologies in advance as I would like to pick your brains about your fitting the Nanni engine.

In May I bought the Bluebelle from Crosshaven (you may be familiar with her), and apart from the aft cabin she seems to have a very similar configuration to Mulroog K. Like you, I have found that just as she starts to become stable the Perkins (which is a brilliant engine) runs out of puff. Researching a solution I came across this thread on the YBW forum and thought that not only did it offer a good solution, but it was practical as it is something that has actually been done rather than an idea on a drawing board. I would consider either the Nanni 320 or 350, both being the same engine in physical dimension (I think). Can you give me any advice, pitfalls to avoid, etc. Also, I think that it's just over a year since you've done this work; what has been your experience in that time?

I am not an engineer, so have very little understanding of turbo back pressure or throttle grungle wheel grease nipple valves, although my day job is as a ship's captain!

FYG I am really looking at the speed increase in order to increase the practical range, with a view to a 5 hour trip to S. Uist from Crinan and then another 3 hours to St. Kilda. There are lots of boats for sale, but a Nelson with 20 knot cruise is probably one of the safest to contemplate this if the weather turns nasty.

Many thanks for any help, guidance, photos, etc that you can pass on.