Bigplumbs
Well-Known Member
Yes but water will move back at speed and allow the prop to turn. You are sort of suggesting that if the boat is prevented from moving forward the prop will not turn at all
How mush speed loss due to weed??
- Thread starter markspark7
- Start date
Yes but water will move back at speed and allow the prop to turn. You are sort of suggesting that if the boat is prevented from moving forward the prop will not turn at all
markspark7
Well-Known Member
The prop is nice and shiny but it does have a bit of green weed, no barnicles though.
im antifouling it next week before i do anymore engine work so will be interesting too see the results from antifouling alone.
I have to say im very surprised at the amount of reduced speed you've all reported.
Bigplumbs
Well-Known Member
Yes that is my point is it not. You say the engine span up was it to normal or just below normal revs. In the OP,s case it is loosing 1200 revs or over one quarter. I still say if the prop is clear ( easy to check) the revs should be just below normal at Wot regardless of the weight or amount of foul on the Hull
longjohnsilver
Well-Known Member
Potentially a huge amount, certainly enough to stop you planing.
rafiki_
Well-Known Member
No, not saying that, but if the prop is fouled, it loses much of its design efficiency, as the fouling causes a lot of drag, as does a fouled hull. Have you tried pushing a car with the brakes on?
darrenw
Well-Known Member
No, I said it wouldn't spin up - it just bogged down. I didn't take note of the RPM, but it was well off WOT and it was clear to hear that it was struggling. Wouldn't even get on the plane. The prop had a few crustrations, but the main culprit was the weed on the bottom of the hull. I also cleaned the water line with a brush, but to no avail. So in my experience, yes, that alone can have a huge impact, as my speedboat was anything but.
CLB
Well-Known Member
In three months my boat went from 30 knots to 10 knots, with a corresponding drop in rpms, all due to barnacle fouling on the hull.
lionelz
Well-Known Member
With all this weed growth lack of performance, lack of efficiency, poor fuel economy and all the other issues makes me happy that I have my boat on a dry stack. In the long term it must save me some money. My anti foul is all but off but I suppose no need for it as it gets jet washed every weekend
Whitelighter
Well-Known Member
I've experienced it on 5 boats, loads of people telling you how it is.
Of course our experience is all wrong.
To the op - either clean the boat and try it or spend loads diagnosing bigplumbs engine fault. Your call
MapisM
Well-Known Member
Well, by the same token, you are suggesting that if the boat is firmly tied to the dock you could engage the forward gear, hammer the throttle and achieve the max rpm, because water will "move back" anyway - as if moving water wouldn't take any effort (i.e. power). :ambivalence:
It was reassuring to read that you fly RC planes rather than jetliners, because in your comparison you completely missed one point that no proper pilot would have overlooked: the density of the medium where a prop is spinning.
There's a not so tiny difference between air and water, you know...
Bigplumbs
Well-Known Member
If you read back I never said to spend loads of money on anything. There are always things you can do for yourself before throwing money at a problem and of course cleaning the boat is a very sensible step.
At no point was I unpleasant in my comments so was wondering why you felt the need to be. People can take an opposing view you know.
Dennis
Spi D
...
Some of the theories presented are interesting but unfortunately have no connection with real life. Quite opposite to to input from people with experience.
It is one deciding factor that the engine is making the rated hp for any calculation to make sense. If a faulty engine makes only a fraction of it's nominal hp you would of course see a drop in speed but in the OP's case all apparently is well.
Wouldn't it be a no-brainer to clean the thing and see what happens? If it makes 4200 rpm again the validity of advice here will be clear and the only consideration will be to pitch down to achieve the recommended rpm range.
The idea of water being pushed away: Would be true if water moved lightly enough to make almost no resistance at all to the prop. As a consequnce, no prop would ever be able move a boat or ship forward (!?), which indeed is a known fact that it does.
The comparison to RC planes: Water has a density of 1000 kg/m^3. Air, at sea level has a density that averages 1.275 kg/m^3. Therefore air is 784 times less dense than water. In this you will find the reason for the very different design of boat/plane props and the thrust produced. Another interesing aspect is the hp/load ratio and the fact that a plane need speed to generate lift whereas a boat need propulsion to move only - and happily does at even the lowest speed.
Give this some thought: You push your boat along the beach by hand, fast as you can. Would you expect it to be harder if you tied a 2" deep 30x10' rya carpet behind the boat and were walking through seaweed?
It is one deciding factor that the engine is making the rated hp for any calculation to make sense. If a faulty engine makes only a fraction of it's nominal hp you would of course see a drop in speed but in the OP's case all apparently is well.
Wouldn't it be a no-brainer to clean the thing and see what happens? If it makes 4200 rpm again the validity of advice here will be clear and the only consideration will be to pitch down to achieve the recommended rpm range.
The idea of water being pushed away: Would be true if water moved lightly enough to make almost no resistance at all to the prop. As a consequnce, no prop would ever be able move a boat or ship forward (!?), which indeed is a known fact that it does.
The comparison to RC planes: Water has a density of 1000 kg/m^3. Air, at sea level has a density that averages 1.275 kg/m^3. Therefore air is 784 times less dense than water. In this you will find the reason for the very different design of boat/plane props and the thrust produced. Another interesing aspect is the hp/load ratio and the fact that a plane need speed to generate lift whereas a boat need propulsion to move only - and happily does at even the lowest speed.
Give this some thought: You push your boat along the beach by hand, fast as you can. Would you expect it to be harder if you tied a 2" deep 30x10' rya carpet behind the boat and were walking through seaweed?
colhel
Well-Known Member
I'm absolutely convinced the problem is down to too much weed.... (he says with a smirk).
Reading between the lines I suspect the OP could do with some tips on antifouling the new boat ie using different anti foul for the drives if necessary and tips on getting it nice and neat and height above the waterline.
Reading between the lines I suspect the OP could do with some tips on antifouling the new boat ie using different anti foul for the drives if necessary and tips on getting it nice and neat and height above the waterline.
markspark7
Well-Known Member
Just a bit of an update.
The bayliner chap rang me this morning after reviewing the infomation stored on his fault code reader and said that their may be an issue with the throttle switch .
apparantly the sometimes stick fooling the engine management system into thinking that its in neutral so limiting revs to 3000rpm.
Anybody had a similar occurance??
The bayliner chap rang me this morning after reviewing the infomation stored on his fault code reader and said that their may be an issue with the throttle switch .
apparantly the sometimes stick fooling the engine management system into thinking that its in neutral so limiting revs to 3000rpm.
Anybody had a similar occurance??
vas
Well-Known Member
oh, comeon now!
you're spoiling all the fun with this comment
We all (bar bigplumbs) concluded that it's weed that's your problem, don't go around now!
serious, I've no idea on this throttle switch, but for sure you'd expect a serious loss of performance due to underwater vegetation. Good luck with the antifouling!
cheers
V.
Bigplumbs
Well-Known Member
Interesting !
markspark7
Well-Known Member
I did think that as i wrote it... i do like a good discussion..oh, comeon now!
you're spoiling all the fun with this comment
We all (bar bigplumbs) concluded that it's weed that's your problem, don't go around now!
serious, I've no idea on this throttle switch, but for sure you'd expect a serious loss of performance due to underwater vegetation. Good luck with the antifouling!
cheers
V.
I,m not convinced myself about the throttle switch however i do feel that there is something holding it back electronically.
I wish i could get it scrubbed and painted just so i could prove it one way or another.
Bigplumbs
Well-Known Member
Believe me you ain't loosing 1200 revs cos of stuff on the hull. Also is it spot on 3000 you are getting if so that tells you something
Dennis
Dennis
markspark7
Well-Known Member
with WOT i was getting 3100 max doing 15 kts but when we lifted outdrive up but still in gear (not ideal i know) it went up to 3500. would also do 3500 in neutral before limiter warning beep went off.
nigelmercier
RIP
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I've found that weed makes me lose track of time, so probably won't notice any difference in speed.