princess 385 performance

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rosssavage

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Hi all... a very typical question. My Princess 385 is fitted with Volvo Tamd 61A's (306bhp apiece) but only makes about 17knots (GPS - so roughly accurate!) at full power. This seems rather slow to me, but I can't find any information detailing the expected full speed. The Fairline turbo 36 with the same engines makes approx 27 knots, and weighs almost the same, so I suspect something is wrong! Any help, much appreciated... ross
 
I have a Fairline Phantom 38 which is 2 tons heavier and has only 110 bhp more power this gives me 30knots. When was the last time your bottom was scrubbed (excuse the question!!!). It does seem rather slow for the available power.
 
I'd expect circa 25 knots.

The first two questions are what revs is she pulling and when was she last antifouled?

61's should pull 2,800 - 2,900 and the tachos should be reading the same, if one is down a bit on the other then you have a "sick" engine being pulled along by the other. If both the same chances are the engines are ok (unlikely to both be "sick" by the same amount) so more likely to be wrong pitch/size props or more likely a weedy bum (the boat, not you).

Even heavy slime will knock loads off the top speed.
 
First question. Are the engines pulling their rated maximum rpm on both sides? If not, then could be dirty hull, dirty props, damaged props. When was the last time you had the boat lifted, scrubbed and antifouled? If the hull and props are clean, then possibly you have an engine related problem so you need to get them checked by a competent engineer. Are there any symptoms of engine problems such as overheating, low oil pressure, smoking at speed or unburnt fuel in the exhaust. Are the fuel filters in good order?
If the engines are pulling their rated rpm, then could be prop size related. Are these the original props? If you know their pitch and diameter, it's worthwile phoning a prop company like Steel Developments and ask them to comment on whether dimensions are appropriate for boat and engines
 
Dirty bottom/props, maybe props incorrectly pitched. Did it use to go faster, does it reach full revs? Maybe air filters blocked but would put money on fouling causing the problem.
 
Would agree with the Deleted User sumary.
I have a P38 (basically the same boat as yours) with 188 mermaid engines which give 22knots max and 17 cruise.
If you are getting full revs, I would suggest that the props have been under pitched, this is usually done for one of two reasons. The first reason is to to maintain engine revs at a slower speed (for extended river use) but the second popular reason is a little more concerning but need not be suspected at this early stage.

Hope this helps
 
Thank you all for your advice... Boat was lifted and antifouled in march last year (so maybe a bit dirty now..) Longjohnsilver, the boat was used exclusively on the river for a few years before I bought her, it was only when I took her out thru the Thames estuary in sep / oct last year that high engine power has been used for years I suspect, so don't know what previous speeds were... The engines rev to 2800 or thereabouts from memory, so they seem ok. I was given a spare pair of props when I bought the boat, so there is every possibility that I have non standards props now fitted... which leads to the next question.. does anyone know off the top of their heads what size / pitch they should be? I will try Steel Developments if know one knows (thanks Deleted User..) Rufus99, although I shouldn't be concerned about the second reason for under pitched props right now, do you mind elaborating?? Scared now...
 
In that case I think Rufus is probably barking up the right tree. But it's worth giving the hull a clean and re anti foul at the same time so you know exactly where you are.
 
The amount of gear/people/fuel/water and may be punching the tide (3-4 knots)plus a little bit of fouling can knock down your top speed down.If you brimmed the tanks before your estuary trip and add a few bods plus bits and pieces and you could add a ton or two to your weight.
Would be inclined to strip out all surplus stuff(booze/TVs/canned grub/outboards/portable gennies) and perhaps get tanks less than half full and have another go before worrying about any serious likely to be expensive grief.?
Nice pix here Princess 385
 
Hi Ross
Before you go to steel developments I would first establish what reduction gearing you have on your gearboxes. Once you know that call them and they should be able to tell you the correct props for the boat and the max speed. Then check your spare props to see if they are the same or similar to what they say. If they are different they should be able to re-pitch them to suit --alot cheaper than new props. For the record I had a 1991 Phantom 38/41 with 61a`s which with a clean bum achieved 25 kts at 2800 revs. It was a heavy boat too being nearer 43ft.
 
Re ; Other reason for reducing pitch.
Not a common problem with Volvo but certainly is with other engines that will remain nameless (O go on then - the 425 yellow things)
Some engines (not just the yellow ones) are prone to overheating. This is not just a design fault, it can be for any number of reasons - poor maintenance, harsh use, general wear etc.
By reducing the pitch, it effectively reduces load and gives the said engine an easier time as without being too technical - load puts more stain on the engine than revs.

From what you have described, I would be amazed if this if this is the case here - the clues here being 61s not known for this, mainly used on rivers in the past and not forgetting the dirty bottom!
The other point I would make is if Princess has spent a long period on rivers the the engines may well be a little choked up inside and this may take a few trips at higher load to clear through.

I hope this post is not one of 'Light the blue touchpaper' jobbies!

Hope this helps
Rufus
 
Rufus99, thanks for expanding on that!! Engine temps are fine (I think!) Ran flat out for about 4 hours on my estuary trip, and all T's and P's were well within the limits. Guess its a trip to the crane with fresh paint and a check on the props... Thanks for all your advice!
 
It might also be worth checking that your props for corrosion, I had a problem similar to yours when our boat was only 6 months old. It transpired that the edges of the prop's had suffered from galvanic corrosion and although visually they seemed fine the performance was down by 8 knt.
The dealer replaced the prop's and everything was fine.
Incidently we have a Jeanneau Prestige 36 with Volvo D6's (310 hp) and we get 32 knts over the ground
 
Good luck with your experiments - I am sure all will be fine and I would be interested to know the outcome.

Incidentally, I have just spoken to a friend of mine who has a P410 with 61A,s fitted.
Depending on loading (Fuel, water, crew, beer etc) he achieves between 25 and 28 knots max and cruises 3 -4 knots below that.
I would think that your 385 should be in the same ballpark.
 
Had a P385 with I think TAMD 60Cs back in 86. When New it Made 28knots flat out tabs adjusted etc.It seemed like a speedboat after the P37..Apart from the gearbox packing up and the shafts needed two replacements by Projects a great boat..Id have one again if I could aford it (Retired) but thats life
 
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