Reprop for more speed?

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Deleted User YDKXO

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The manufacturer of my boat (Ferretti) reckon that my boat should do 28.5kts flat out @ max rpm of the engines (2800). In fact, in the operating manual, there is a speed/rpm graph and a statement that a Ferretti 46 with the same engines as my boat has been tested with full fuel and water tanks, 9 people + 400kg of extra weight on board and it achieved 28.5kts in an ambient temp of 15degC
When I bought my boat in Holland, I sea trialled it on the Isselmeer and it reached 27.5kts max but the boat had been stored ashore for 18 months and I reasoned, maybe wrongly, that after a service and a bit of use, it might achieve a bit more
Then I moved the boat to the Med and in Med conditions, the boat has never achieved more than 26kts at max rpm even with a clean hull and sterngear and lightly loaded and a lot less with a dirty hull. I've not been unduly bothered by this because I'm happy cruising in the 18-20kt range but it has occured to me that if I could improve the boat's performance in line with what the manufacturer says it ought to do, then not only could I increase it's speed but also the fuel consumption which, given the increasing cost of diesel, might be worth doing
At present, the boat will only rev to around 2600-2650rpm which is 100-150 rpm shy of the rated max rpm. The engines have been checked and serviced and pronounced to be in good health and the rev counters appear to be accurate so that just leaves the props. My question is this. Does the panel think that it would be worthwile considering repropping to increase the rpm and would this involve modifying the existing props or getting completely new ones?
 
if I am not wrong the Ferretti 46 is equipped with Volvos 480
which tend to loose a bit of there top end over time, more then the Cats
still I think if you can squeeze those 150 rpm I think 27 knots is possible, if 26 knots are being clocked with at 2650 rpm

if the engines are perfect then it might have smaller pitched properllers cause it was used delivered for Northern Waters.
Did you ever checked with Ferretti about standard properllers for med delivered boats?
Check also if you might have some piting on the properllers, as underwater exhausts can make this more likely....
Ferretti use very expensive high quality Rolla Properllers for there 15 mts + models and Radice also very good but less expensive props...
Rolla cost almost double to everything there is on the market!

I tend to believe Ferretti speed figures as very correct or close to the truth as in my experience, with not more then 1 knot difference here and there for a loaded boat...
 
Poweryacht, my boat has Cats. The props are in good condition with no sign of pitting or damage. But it is possible that you may be right on the size of props. My boat was delivered to the first owner (a Dutchman) in the Med but then he moved it to Holland and used it there for a couple of years so it is possible that the props were sized for N Europe waters originally or he changed them
How do I find what size the props should be for the Med? Do Ferretti have a technical dept that customers can speak to?
 
Hello Mike,

I think you should contact them on the site, usually they are very helpful or try to phone them up on Monday and ask for there service department....

you can go on www.ferretti-yachts.com and leave a message on the contact us and then click service department
in my experience Ferretti have among the most attentive after sales service
I think you can also try Ventura or the guy you bought the boat from if he is / was a Ferretti dealer, may be like that you can know more a bit of the history of the props
if the engines are perfect, and props are ok, it might be too much paint is slowing the boat....
BTW are the props painted?
 
Have you any black smoke at WOT, if as you say the engines will not reach Max revs and you are clean underneath, then I would suspect you are overpropped, have a word with Paul Williams at Clementsmarine.co.uk, 01234 378814, he is red hot and very good at sorting this sort of problem. I have connection with the above except to say he sorted us out.
 
Have you any black smoke at WOT, if as you say the engines will not reach Max revs and you are clean underneath, then I would suspect you are overpropped, have a word with Paul Williams at Clementsmarine.co.uk, 01234 378814, he is red hot and very good at sorting this sort of problem. I have no connection with the above except to say he sorted us out.
 
My boat consistently dropped from 33kts in the UK to 31 kts in the Med. Water density and air temperature were the cause. Smaller pitch props may help to get a bit of that back, but it's probably not worth the hassle.
 
Well strangely i didn't see any loss in speed moving from UK to med? I'm no expert so this is just an idea, but if the engines are struggling to get enough air anyway, then maybe using them in a hotter climate where the air is less dense would exagerate the problem, and affect the speed. If there is plenty of air reaching the cylinders then maybe less of a problem, so the effect could vary from boat to boat?

Would be easy to check by running with the engine hatch open, and of course make sure the filters are clean.

Only other thought is to have the injectors checked, if they are worn then the spray will be less of a spray and hence less complete combustion, but not sure this would be any different in med to N Europe.
 
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Only other thought is to have the injectors checked, if they are worn then the spray will be less of a spray and hence less complete combustion, but not sure this would be any different in med to N Europe.

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when top end revs go down the injecotrs are to blame first

as for the air intakes it may happen but not I think in most boats, as all of them have more air or less the same air in the engines room

Mike it will be good to know if the boat ever done full revs in the med which, as that might take off the propeller problem

if it is then it might be the injectors or also a Turbo cleaning might be the next case saying it from my PC at home...

CASES
1) Props
2) Hull Paint (too much antifouling over the years)
3) Turbos (over the years epecially if boat is used at lower revs these might be blocked with carbon hence lower the top output)
4) Injectors
-----
5) you have a dolhin who grabs with the boat each time you try to give it top speed /forums/images/graemlins/tongue.gif
 
It is my understanding that a small loss of speed is the norm, but it is interesting that you didn't experience it.

AFAIK the different air density just results in a lower mass flow to the engine, hence less power.

It was a source of contention between other engine manufacturers and Volvo that Volvo tested their engines at lower temperature and thus claimed higher power.
 
[ QUOTE ]
Volvo tested their engines at lower temperature and thus claimed higher power

[/ QUOTE ]

Well, fair's fair: Sweden is quite cold at times. /forums/images/graemlins/laugh.gif
 
Poweryacht, the props are not painted and I don't think there are that many coats of antifoul on the boat. I think I will try contacting Ferretti direct
 
Yeah but, Ferretti being Italian presumably tested the boat in the Med and they got 28.5kts absolutely fully loaded whereas I can barely get 26kts lightly loaded so I think the comparison is valid
 
Poweryacht, the boat has never achieved the max engine rpm in the Med. I talked to the engineer who regularly services my engines and he does'nt believe that there is anything wrong with the engines although I accept that the engines will lose top end power over the years but the boat is only 7 yrs old with 500hrs
 
Hi Mike
then at this stage with only 500 hours I blame the props, and may be the Turbos with a small percentage...

check with Ferretti the size 200 RPM is a lot IMO and since the boat never did that I presume props are a bit big
if I am correct the props on your boat should be Radice, I think 2 replacement props will cost about 4/5000 EUROS if they are ROLLA they will be double that price
 
Two years ago I had the opposite problem in that I would reach max rpm and the governor would cut in.

I took my props to Hamble props who added an inch of pitch.

I gained just over 2 knots in top end and cruise speed.

It was well worth the trouble to do.


As to saving fuel, I dont know.

Once you have a higher cruise speed available you tend to use it.

In effect I got an extra 2 + knots of speed for free, we certainly dont use more fuel so chances are if we slowed down we would save ?
 
Where are you reading the 26knots, GPS or log. My Raymarine Log was 5 knots lower than GPS reading because it had not been calibrated to the boat after installation? perhaps your log need calibration.
 
DAKA, thanks for that. What sort of money did the re pitching cost?
 
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