Calling Trader owners.

[volvopaul]

Im trying to find out from Trader what size props are fitted to a 1991 trader 41 with 2x volvo tamd41 200hp engines in.

I know its not a speed boat but it will do 6.5 knots on one engine but only 8 on both flat out and it makes full 3900 rpm on both.

It sound to me like its underpropped, the owner has repeatedly phoned trader just to get the answerphone all the time.

Just think if he had an order for a new one???????????? pie in the sky I know, hes heard all about them and there past on here he watched with great interest.

Just really looking for a bit of help, also going down the route of asking hamble props and clements for there views on it.

I know that one with 306 volvos will make a good 17knots and up to 20 with the 375 cats in.

Any help appreciated as id rather get some figures from an owner as opposed to a computer generated guidance.

 

[PaulGooch]

There's a Trader on the hammerhead next to where i berth Paul. Not sure of any details, but we should be going down at the weekend, he's usually about, in which case i'll see what i can find out.

 

[Latestarter1]

Trader speed estimate

Working the numbers long hand having been brought up using Crouches method, which is viewed as only good for estimates in todays computer aided world I come up with the following, hence the health warning;

Assume Volvo TAMD41P/HSW63 has 140 kW (191 SAE Hp) at the propeller.

Trader displacement with light engines, say 14 Tonnes.

Waterline length say 11.3 Mts

This SHOULD give a comfortable cruise speed of 12 knots, I do not have a 41P curve to hand but assume this would be about 400 rpm 'off the top' with about 14 knots at WOT.

I do not know what wheel a Trader spins but assuming it has 2:1 box three blades 19X13 absorbes the correct amount of power.

Now for the big spanner in the works....I tried graphing the #'s and they get all screwed up at 8.4 knots, let me explain, using my quick and dirty calculations 8.4 knots appears to be the transitional hull speed, even pulling rated power 140 Kw appears to be barely/perhaps not enough to get over the hump. Add more pitch will only make the situation worse.

Some vessel history would be helpful, it may prove to be a troubled child...

 

[PCUK]

At displacement speed the rough rule of thumb as I understand it is around two extra knots for double the power.

 

[PaulGooch]

The guy i mentioned in my earlier post did tell me a couple of weeks ago that his cruises at 10 knots displacement. He said he never runs it on the plane as it uses too much fuel and he's never in a hurry.

 

[Latestarter1]

Trader

This would appear to confirm the ‘back of a fag packet’ hypothesis.

Using a W/L of 11.3 Metres 8.4 knots is right on the hump anything over this hull is transitioning to planing mode, not operating in displacement mode, therefore the notional 10 knots would sound a good economical speed as actual propeller power demand is both less than higher planing speed and less than climbing the hump at 8 knots.

I have looked at the 41P power curve, does not appear to be a marriage made in heaven...

 

[TheBishop]

Got a Trader 50 with Cats 3208 Turbo. Will rev up to 2600 and bang on at 15kts but you are burning diesel at a rare old rate. We tend to cruise at 1800 which gives us 8 knots..probably displacement speed....but works for us. As an ex yottie I use the tidal atlases as my bible so I look to get on the tidal escalator wherever possible.

Am looking to replace my props next year so have a keen interest in this debate. Any ideas on cost of props??

The Bishop

 

[volvopaul]

Thanks all for replies,

Latestarter, the gearboxes are volvos ms4/5 2.63 to 1 ratio.

Yes when he bought it I had my doubts, one with a pair of nice 120 fords would have been a better bet for his river use and occasional sea work, however revving them up to 3600 to get it up on the plane over the hump I think is near impossible.

Some years back my Father had a Histar 42 which was nearly the same boat without the deep keel, it had 2x375cats in and the revs were bang on at 2800rpm giving a creditable 22knots flat out but the fuel burn even at cruise 18 knots at 2600rpm we could not like with 0.6mpg average.

Imagine my face when we used 80 gallons to travel from southampton to weymouth, that was in the days when you could fuel up in weymouth for 11p per litre!!!.

The owner is talking to cjr, hamble props and clements at the mo trying still to get a reply from TC at trader.

 

[ulyden]

If you have 3900rpm 2.63 gear and 19*13propeller it looks like this!

Propeller speed (3900rpm /60*2.63) *13*0.025m= 8m/s or 15knots

assuming 25% slipp or more you shold be at 11knots or less!

So if you have this gear ratio and 13 inch proppeller you cant get it into 20 knots!

Then you need 25knots propeller speed and max 25% slip =19knots

That means a pich of 21inch!

 

[Latestarter1]

Trader

Volvopaul,

Volvo MS3/4 2.63 brings shaft speed down to around 1,500 rpm, nobody would willingly go oversquare, 19 X 21 and Trader 41 looks like it swings larger wheels so 21.5 X 17 would absorb the correct anount of power.

Your problem is without a bang on weight, my ##'s based on 14 tonnes you are having to run around like a one legged man at an ass kicking party. Published displacement is no use to you, an accuate recent weight is vital, what may have worked in 1991 will not work now, age and putting on weight go hand in hand.

Still no vessel history, logs etc, could be one of those situations where you are crusing for a bruising..

 

[Piers]

Hi Volvo Paul,

Knowing you are a boat engineer by trade and therefore an expert whilst I am only an enthusiastic owner, might I throw in my two penny worth?

The first qn I'd try to find out is whether the props have ever been fiddled with in the past. If so, might it have been done to cover an engine problem?

Then, I'd ask if 3900 is the Wide Open Throttle (WOT) rating for those engines? If it's higher, the engine's control systems may be 'de-rating' the power output to protect the engine. So although the rpm looks high, the engine is operating at less than its design HP.

If 3900 is spot on (by the way, has a check been done to check the instrument showing 3900 is actually 3900?), do the temps stay good for a 30 min run at WOT? Many clues come out if this test cannot be sustained.

For example, if loads of black smoke pour out, are the engines being overfuelled etc etc.

However, assuming all is OK, and yes 3900 is WOT, and the hull's clen and the boat isn't carrying excessive weight, I would only then start looking at the props.

If 3900 isn't WOT, then I'd start to look at the following before challenging the props,

- Exhaust back-pressure?
- Can Air and Fuel flow without obstruction?
- Fuel injection system
- Valve adjustment

Forgive me for teaching Gran to suck eggs....

 

[Latestarter1]

Tader

'Forgive me for teaching Gran to suck eggs...'

Piers, I would respectfully sugguest you are...

Absolutely no personal connection with Volvopaul however reading between the lines the very fact that mention was made that the 41P's were making spec sheet rated rpm (3,900) is sufficient inference that he is quite happy with engine performance.

I would be very surprised if the basic stuff you mention had not already been carried out, evidenced that engines can actually make WOT loaded.

You are quite correct and in general agreement with me that the vessels history is the key, however another very good reason for pre-purchase sea trials. I suspect Volvopaul has covered all basics and is attempting to gather some evidence from a similar vessel, however has to be powered with identical engines to be relevant. I did not read into the post that there was a desire to start ripping into the props, just seeking an insight.

These engines are old generation plain vanilla mechanical motors, you understanding of electronically controlled engines is a little flawed. Yes electronic engines can measure % load,which in this case would be a doddle, plug in the laptop and one would have a nice graph telling you what the propeller is asking the engine to do as various vessel speeds.
There is one drawback in your logic, electronic engines know what load is being placed upon them up to 100% however the algorithm cannot calculate % overload therefore there is no system de-rate as a result.

A distance view as a 'couch engineer' is that this vessel is a potential lemon, marginal power plants may have worked, just in 1991, however like us all gained weight in latter years, and now has to be considered a displacement speed vessel and nothing more. Sea trial. sea trial, sea trial.

 

[volvopaul]

Hi Volvo Paul,

Knowing you are a boat engineer by trade and therefore an expert whilst I am only an enthusiastic owner, might I throw in my two penny worth?

The first qn I'd try to find out is whether the props have ever been fiddled with in the past. If so, might it have been done to cover an engine problem?

Then, I'd ask if 3900 is the Wide Open Throttle (WOT) rating for those engines? If it's higher, the engine's control systems may be 'de-rating' the power output to protect the engine. So although the rpm looks high, the engine is operating at less than its design HP.

If 3900 is spot on (by the way, has a check been done to check the instrument showing 3900 is actually 3900?), do the temps stay good for a 30 min run at WOT? Many clues come out if this test cannot be sustained.

For example, if loads of black smoke pour out, are the engines being overfuelled etc etc.

However, assuming all is OK, and yes 3900 is WOT, and the hull's clen and the boat isn't carrying excessive weight, I would only then start looking at the props.

If 3900 isn't WOT, then I'd start to look at the following before challenging the props,

- Exhaust back-pressure?
- Can Air and Fuel flow without obstruction?
- Fuel injection system
- Valve adjustment

Forgive me for teaching Gran to suck eggs....

Hi Piers, thanks for you input.

Only on here as not at boat today, missing the first great weather window due to family stuff.

The engines have been partially stripped, heads off, valves refaced upper end overhaul, all coolers stripped reasealed and descaled using rydelime, so absolutely no cooling issues.

All injectors tested and reset, all oil leaks and a general full service carried out, so im 100% sure the engines are fine for there age.

Im just really trying to do my job and best for the owner, ive seen photos of the props they look the right diameter but as latestarter has said im trying to find out what the boat would either have left the factory with, or find an identical owner with a boat and same engines that can honestly say where we should be, as to what diameter and pitch we should have to give a sensible speed.

From the owners input it sound to me like the pitch has been changed dramatically, or maybe at some point in the boats life its had a grounding and someone kind person has come along with 2 new props being the good samaritan and fitted them in hope it will all be ok.

As said it will make 6.5 on one engine but barely 8 on both at 3900 rpm, to me its seems like they are spinning 2 egg whisks!.

The other issue could be that the gearboxes are the wrong ratio, I was horrified to find the ms4 gearboxes there in the first place id have thought that chappel would have done the first owner a proper favour instead of penny pinching and fitted a proper hydraulic gearbox for little extra cost.

Yet to date have we had a reply from trader, yet if we were looking for a new boat it would be im sure a differnt response.

 

[PaulGooch]

Just a quicky Paul, as sods law would dictate the guy in my marina with the Trader wasn't there today. He's been there that last few cold weekends though lol. I'll keep an eye out for him next weekend, if you don't get sorted in the meantime.

 

[ulyden]

Strange case! Point is! If the boat have the original propeller and gear it have to have been totally wrong all the time! If the propellers had no slip the speed had been 15knots! So more than tat is impossible! Less than 20% slip is unrealistic and that means 12knots! If all the 380hp is fully used and the speed is 12 knots its ok!

Now when the boat is old and hull is not like it was and heavier than original the speed is 8 knots. Engines are still running 3900rpm! Strange!

If the propeller was ok when the boat was new the slip has increased to amazing 45% now! If you know propeller theory the trust and the torque
Always increase with increasing slip.(se upper part of picture) That means that at the same engine speed the torque is much higher now! Power is product of torque multiplied with the engine speed (Radians pr second) If the torque is higher the maximum torque for this engine the engine speed will drop until balance between engine torque and propeller torque.

So if the boat speed is going down the engine speed is dropping as well!

On big ships the propeller is always 5% or more below engine max torque at full speed! This is because the ship speed will always drop in between the dockings! If the propeller was consuming full power at full speed whet it was new the engine had been overloaded most of the ship life time!

So I also think that gear ratio or propeller pitch is wrong! Engine is ok!

By slip I mean difference between propeller theoretical speed (if the water was cheese!) and the boat speed!

Any good English word for it?

 

[Piers]

Hi Piers, thanks for you input.

Hi Volvo Paul,

Thanks for your comments. As you say, it's a shame an hydraulic gearbox wasn't installed in the first place (I love my TwinDiscs which work with Cummins 6CTAs!).

All the best in 'the hunt for the lost knots'. Do please let us know what the final result is.

(Piers returns to suck his own eggs...)

 

[TraderCliff]

Trader Speed Issue

Hi… Thanks very much for all the replies and comments. I am the owner of the Trader 41 that VolvoPaul has been, and is currently working on again, rebuilding our Starboard engine after a recent trip to Hull. This was our first trip out in the boat since we bought her back in October last year.

She was bought from an elderly gentleman in Plymouth who had owned her for some six years or so. I got the impression that he just used to potter around in her with his mates.

This is the first time we have opened her up to see what she would do, and as mentioned by Volvopaul 7 – 7.5 knots is the max with both engines achieving full rev’s.

To help with some of the calculation is can confirm that when she was lifted onto the trailer the strain gauge showed a weight of 11 tonnes, and just been re-antfouled, so has a clean bottom.

We appreciate she is an old lady now and may have lost some of her puff, but with the work Volvopaul has recently done on the engines we were hoping to get close to at least 12 knots, too which we would be very happy.

Having recently spoken to First Marine and Clements concerning the props that they would recommend the following was suggested. Both companies suggested that 12 knots should be entirely achievable.

24 inch Dia
22 inch Pitch

22 inch Dia
24 inch Pitch

With Clements saying that when running on one engine you should not be able to get anywhere near full revs and approx 2,800 is more realistic. Only with both engines running should you be able to achieve full rpm, and so full speed.

Again as previously mentioned by Volvopaul this is not the case here. On one engine we can achieve almost full rpm, with a speed of approx 6 – 6.5 knots, and with both engines running only increase this speed by 1 – 1.5 knots.

Once the engine has been rebuilt we will have to carry out further rev / speed tests, which I am sure will result in having to take her out the water to establish the exact details of the props currently fitted.

As a layman to all the technical stuff, it just sounds and feels like the wrong props are fitted. Full revs are being achieved very quickly on one or both engines with limited speed. I suspect that as full rpm is being achieved on one engine maximum speed (for the props) has also been achieved, hence very limited increase when running two engines.

Have attached a photo of the props which dont look to small to me, so guess the pitch is now in question.

Thanks for all the comments, and continue to watch with interest.

 

[Latestarter1]

Now we have a displacement of 11 tonnes Vs 14+ tonnes change in D/L Ratio makes an exponential difference, I picked up 14.5 tones off spec sheets of larger engined Trader 41's. The small engines obviously make a large inpact on displacement.

With this infomation 12 knots cruise, at about 400 off the top should be a no brainer.

Never heard of First Marine, however I bet Paul at Clements came up with the 24's he likes big wheels, which does make perfect sense at these speeds, however will this still give you a minimum of 15% tip clearance?

Both options are just slightly agressive in my book, prop guys always look at out of the box performance, and make no allowance for end of season weed growth leading to engine overloading.

 

[TraderCliff]

Thanks Latestarter1, your comments are very much appreciated, and yes it was Paul from Clements who came up with the 24’s. At this time I don’t know about the prop tip clearance and will have to have the boat out of the water to check this, and the prop size etc out. However my gut feeling is that 24's will be to big.

When you say slightly aggressive what would you recommend? assuming the 24 inch are to big in terms of clearance.

I assume the bigger the prop the less pitch is needed..

Again as a layman and from the comments made on this topic, I was thinking in terms of 22 inch Dia. With 23 inch pitch?

 

[Latestarter1]

Both pitch and diameter absorb the torque generated by the engine; however diameter is by far the most important factor. Thus the ratio of two, to three inches of pitch equals one inch of diameter is a reasonable guide, however it is no more than that, just a guide, and you should never select a propeller based on this rule alone.

On twin screw craft tip clearance is easily measured (Remember that the shortest distance may not be straight up, swing your rule through an arc centred on shaft centre line). As your vessel probably has an SL Ratio of about 2.5 you must have AT least 15% tip clearance. However you are faced with the trade off between the increased efficiency of a bigger wheel v/s increased efficiency of improved water flow and reduced vibration. In my book go down to 15% maybe 17 % for comfort, tip clearance as the largest diameter. No risk of rumble rumble.

My concern is that ALL prop shops are a tad too aggressive on pitch, wanting to pull 100% load out of the engine and never seem to allow for ‘marine aging’. If you had electronic motors I would shoot at pulling about 85% engine load squeaky clean at the beginning of the year in order that engines not overloaded at the end of the season.