Portofino
Well-Known Member
Sorry missed off "in a vacuum "
Any how its the speed over the water kinda -horizontal
which is what the OP was on about
Does everyone lie about boat speed?
- Thread starter Barleycorn
- Start date
Sorry missed off "in a vacuum "
Any how its the speed over the water kinda -horizontal
which is what the OP was on about
wingless
Active Member
Those numbers are correct for passengers who fall overboard during my free-fall plummet to Earth.
http://en.wikipedia.org/wiki/Terminal_velocity
My boat weighs 18,000 pounds dry, 24,000 pounds fully loaded, significantly more than a 200 pound passenger (about 100X), so my terminal velocity is going to be MUCH higher than for a passenger who falls overboard, even w/ the larger area and the larger drag coefficient.
Barleycorn
Well-Known Member
Went to the boat yesterday. Bought a tachometer, but unfortunately couldn't get to the crank pulley as it was guarded, and I never had a socket set with me. (Made mental note to remove the guard, don't fancy it at sea if I have to change the alternator belt).
Anyway the engine revved up to 2900 in neutral at WOT according to the panel gauge, and the throttle goes up to the stop.
I changed the diesel filters, and went to sea. Sadly under load she still only revved to 2200. Only thing is even at 2200 there was no black smoke, only white / steam.. Had it been an over propping problem I would have thought that she would belch out smoke, I know it would with a tractor back on the governer under load.
I am going to check if there's a pick up gauze in the diesel tank today, and have ordered a new lift pump.
Anyway the engine revved up to 2900 in neutral at WOT according to the panel gauge, and the throttle goes up to the stop.
I changed the diesel filters, and went to sea. Sadly under load she still only revved to 2200. Only thing is even at 2200 there was no black smoke, only white / steam.. Had it been an over propping problem I would have thought that she would belch out smoke, I know it would with a tractor back on the governer under load.
I am going to check if there's a pick up gauze in the diesel tank today, and have ordered a new lift pump.
longjohnsilver
Well-Known Member
It's your prop! I'd bet my house on it. Tinkering elsewhere won't make much difference, although having a spare lift pump could be useful, it's the only failed item that necessitated me having a tow back in.
Latestarter1
Well-Known Member
Barleycorn do not be in denial you are way over propped, sounds like the weight you gave me was correct. Carry on like this and you will end up with engine damage, EGT is sky high.
Characteristics of DPA pump on your engine is such that overload will not black smoke, you have me worried re white smoke B210 should be clean. This engine is also an 'honest' rating, develops 210 'proper' hp at 2,600 rpm compared with say a Perkins/Sabre M225 which develops around 195 hp at 2,500 rpm.
Get that belt guard OFF it restricts air flow to alternator and causes diode failure in high hour applications. Remember to replace guard mounting bolts and be careful of bottom one, put a washer under the head or it will bottom out and leak lube oil. A well maintained Polyvee belt does not fail if inspected however the guard puts it out of sight out of mind.
I will do calc based on 5 tonnes however accept boat will never be the Starship Enterprise.
Characteristics of DPA pump on your engine is such that overload will not black smoke, you have me worried re white smoke B210 should be clean. This engine is also an 'honest' rating, develops 210 'proper' hp at 2,600 rpm compared with say a Perkins/Sabre M225 which develops around 195 hp at 2,500 rpm.
Get that belt guard OFF it restricts air flow to alternator and causes diode failure in high hour applications. Remember to replace guard mounting bolts and be careful of bottom one, put a washer under the head or it will bottom out and leak lube oil. A well maintained Polyvee belt does not fail if inspected however the guard puts it out of sight out of mind.
I will do calc based on 5 tonnes however accept boat will never be the Starship Enterprise.
wingless
Active Member
Unless you go through the planet,as it is breaking up, before engaging the Hyper Drive, assuming the bottom is clean and the prop pitch is correct.
https://www.youtube.com/watch?v=ZDi_61LYEHs
oldgit
Well-Known Member
Rumour has it that some boat builders sent boats for testing with anchor chains that might just be enough to reach the bottom of a small shallow bath ?
Barleycorn
Well-Known Member
Thanks again Latestarter.
Went out on the boat over the weekend. There was no filter in the diesel pick up, so OK, I'm over propped!
Thing is, I cruised at 2000 RPM, which gave me 8 1/2 knots through the water. I met another Aquastar 27 owner in Poole, and he again cruises at 12 knots, but he had a Volvo engine which revved a lot higher, he cruised at 3000 RPM.
So if I reduce the pitch on my prop, so to get this theoretical 12 knots, I will probably be running at around 2500 RPM. So will this drastically effect my MPG, or am I using more diesel now as it is overloaded? (I had a good look at the exhaust, and it was dark grey).
I look forward to your size recommendation, thanks again for your trouble. Really having trouble getting my head round this!
Went out on the boat over the weekend. There was no filter in the diesel pick up, so OK, I'm over propped!
Thing is, I cruised at 2000 RPM, which gave me 8 1/2 knots through the water. I met another Aquastar 27 owner in Poole, and he again cruises at 12 knots, but he had a Volvo engine which revved a lot higher, he cruised at 3000 RPM.
So if I reduce the pitch on my prop, so to get this theoretical 12 knots, I will probably be running at around 2500 RPM. So will this drastically effect my MPG, or am I using more diesel now as it is overloaded? (I had a good look at the exhaust, and it was dark grey).
I look forward to your size recommendation, thanks again for your trouble. Really having trouble getting my head round this!
Momac
Well-Known Member
Seems to me you should stick with 7 knots to get sensible fuel economy.
Latestarter1
Well-Known Member
Barleycorn for gawd sake stop comparing similar boats with different engines, rated speeds and transmission ratios. And here we go yet again 'propellers move boats engines merely turn them!'
Looks like you have heavy vessel for just 24 ft LWL any small changes in displacement have a major impact on propeller demand. Just think about Volvo Penta powered similar vessel. Say engine is a TAMD 41 with a nominal 200 hp @ 3,800 rpm with Volvo Penta transmission. You have significantly heavier propulsion package with the Cummins B210 ZF IRM220 A, in a smaller vessel such as this I would have specified a lighter ZF 63A however yard numpties are yard numpties.
Cutting to the chase #1 the owner of the vessel is blowing smoke, 12 knots is hull speed, Lets say VP powered vessel probably has 2.1 reduction box or thereabouts turning shaft at 1,900 rpm @ WOT. If we assume a 2.7 prop exponent at max hull speed circa 12 knots slightly lighter VP powered vessel will be demanding 140 proper hp. Looking at the TAMD 41 curve engine only HAS 100 kW or 140 hp metric at 3,000 rpm, yes a simple case of boat speed myopia and no basis for panicking.
Your continuous cruise speed with Cummins B210 is 2,400 rpm, with shaft speed of just over 1,700 rpm, your propeller demand is just over 140 hp at 12 knots due to heavier displacement but engine still has almost 200 hp proper hp available at this speed.
Get prop graunched down to 19 X 16 3/4 and you you are likely to see results more to you liking and not ragging the guts out of your engine.
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Barleycorn
Well-Known Member
OK, no longer in denial, have joined propellers anonymous!
I will get a quote to get my old propeller cut down as you suggest.
At least with the drystack I haven't got to pay for being hauled out.
It's still nagging me though that the boat came with this propellor, and a new one the same. And the previous owner quoted 10 to 12 knots cruising, 17 flat out. I bought the boat up North, and never met the previous owner.
Thanks again for your help.
I will get a quote to get my old propeller cut down as you suggest.
At least with the drystack I haven't got to pay for being hauled out.
It's still nagging me though that the boat came with this propellor, and a new one the same. And the previous owner quoted 10 to 12 knots cruising, 17 flat out. I bought the boat up North, and never met the previous owner.
Thanks again for your help.
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jimmy_the_builder
Well-Known Member
Could it be however that the numbers the prev owner quoted you were what he expected to achieve, and in fact his actuals were in line with what you're getting? He's then assumed that lack of actual performance is due to a bad prop, which is why you got a new prop with the boat.
Back in the here and now, you'll struggle to get a more definitive answer about this sort of thing than that given by LS1. Now's the time to source a new prop as suggested, or mod one of your existing ones, and once you've got the boat working within parameters you'll soon forget all this new-boat angst.
rbcoomer
Well-Known Member
Can you not borrow a suitable prop to try first? Nothing beats real world testing and even the prop calculators can miss things! I've amassed a small collection of stainless over the last 18 months (all s/h from eBay I hasten to add!) and still not got the 'right' one... I'm certain my props are cheaper than yours will be however so I'd go with the panels recommendations as a good start. 
Mine's a standard prop as its a 90hp Mercury outboard, but perhaps worth sharing my experiences anyway...
I bought the boat (15'9" Fletcher - i.e. fast, planing deep V hull) with a 19p alloy prop. The previous owner used for water-skiing, so hole-shot was important, but for us it's a family boat for exploring and just 'getting out there'. The first issue was that she was stern heavy - so much so that she dug a deeper and deeper hole until almost vertical and doing about 23kts. At this point, the bow would drop and in the blink of eye, she'd be doing 35kts. This is ok on a lake etc, but on the sea where we use, far from ideal as we need speed to match conditions and sensible economy (as soon as we eased back below 22kts, she'd start to drop the stern back in and then drop off the plane). First course was to shift as much weight forward as we could but this had no noticeable effect. I then thought about moving the fuel tank (stern), but this would mean cutting the deck for a filler cap, vent etc so opted for Smart Tabs to give stern lift instead. I had used fins/foils on outboards before, but had read various instances of high speed handling issues so thought the tabs warranted a try. Very pleased with outcome and can now plane from about 15kts.
As I started to use more and weather improved, I discovered that WOT would over-rev the engine - 5500 is max, but I could hit 6000 (36kts) with more to go! Thus onto the props... I watched and bid on loads on eBay, starting naively with 3 blade 'Laser II' as I though the existing one was three blade and that would be the best bet. Acquired a 20p Laser II and could still get 5500rpm/35kts - prop slip seemed to eat up the difference
I should probably have quit whilst ahead at this stage, but high prop slip convince me there was more to give. I then borrowed a friends 19p 4-blade Trophy Plus - much better grip in corners, better hole-shot, and generally more responsive - but... still topped out at 35kts (now 5250rpm which was the 'target'). In the meanwhile I had won an auction on a 22p Laser II, so that needed a try too... 
(this was over the course of last summer whilst sorting out various other gremlins) You guessed it - 5500rpm and 35kts, but bags of slip! (About 22% 
) By this time I was running the numbers, weights etc through a plethora of prop-calculators and two (including the Mercury one, suggested that a Trophy Plus 23.4p was optimal prop, so as they don't do a .4 I searched on a 23p and found one 'as new, unused' for £200. More than I wanted to spend, but by this time the inner speed freak was convinced I could wring out another 4kts on the best achieved so far to get to the magical 40kts... I'd had various fuel issues and a trim problem, so it wasn't until early this year with fixed trim, cleaned carbs, new pump diaphragm and renewed impetus that I could test. Went down to Plymouth Sound with a friend who's a former powerboat racer and, shod with the 23p Trophy took her for a blast. Didn't quite expect the result we got, but (thankfully) with much more knowledgeable friend at the helm, we found that the bite was perhaps a tad too much for choppy water as the boat had a serious lean and wanted to corkscrew whenever we got the hull out! Not ideal for a family boat. Not wanting to start lifting engine etc and more serious tuning methods, I've (almost!) concluded that 35~36kts is enough! Interestingly, we did head up the Plym to the water-skiing area and took turns to sit in the back so we could move to balance out the 'list' and we did get 36.8kts on the GPS at 4600rpm. Shows there's more to go, but into the same overloaded engine situation that you have. I've also since leaned that the Laser II gives bow lift, whereas the Trophy Plus gives stern lift, so maybe need to test again without the tabs - or is that just an excuse to get more testing in? 
In short, you could spend a fortune trying different setups and first attempt may not give what you expect! You certainly appear to need to drop down in pitch in order that engine can reach it's potential and not be overloaded. I suspect as others suggested, previous owner calculated maximum speed rather than achieved it - at least not with that prop! It's easy to play with small boats, trying different setups etc but a 5 tonne vessel is presumably going to be quite expensive if you have to lift out too often! I wondered about more blades to help lift yours over the hump, but without knowing how much slip currently and an accurate idea of setup, dropping a pitch would seem the more viable starting point? You'd also need to drop even lower if you added a blade 16/17p perhaps?
(As for me, I'm looking out for a 20p or 21p Trophy Plus now - not too seriously, but looking all the same...
)
Mine's a standard prop as its a 90hp Mercury outboard, but perhaps worth sharing my experiences anyway...
I bought the boat (15'9" Fletcher - i.e. fast, planing deep V hull) with a 19p alloy prop. The previous owner used for water-skiing, so hole-shot was important, but for us it's a family boat for exploring and just 'getting out there'. The first issue was that she was stern heavy - so much so that she dug a deeper and deeper hole until almost vertical and doing about 23kts. At this point, the bow would drop and in the blink of eye, she'd be doing 35kts. This is ok on a lake etc, but on the sea where we use, far from ideal as we need speed to match conditions and sensible economy (as soon as we eased back below 22kts, she'd start to drop the stern back in and then drop off the plane). First course was to shift as much weight forward as we could but this had no noticeable effect. I then thought about moving the fuel tank (stern), but this would mean cutting the deck for a filler cap, vent etc so opted for Smart Tabs to give stern lift instead. I had used fins/foils on outboards before, but had read various instances of high speed handling issues so thought the tabs warranted a try. Very pleased with outcome and can now plane from about 15kts.
As I started to use more and weather improved, I discovered that WOT would over-rev the engine - 5500 is max, but I could hit 6000 (36kts) with more to go! Thus onto the props... I watched and bid on loads on eBay, starting naively with 3 blade 'Laser II' as I though the existing one was three blade and that would be the best bet. Acquired a 20p Laser II and could still get 5500rpm/35kts - prop slip seemed to eat up the difference
I should probably have quit whilst ahead at this stage, but high prop slip convince me there was more to give. I then borrowed a friends 19p 4-blade Trophy Plus - much better grip in corners, better hole-shot, and generally more responsive - but... still topped out at 35kts (now 5250rpm which was the 'target'). In the meanwhile I had won an auction on a 22p Laser II, so that needed a try too... (this was over the course of last summer whilst sorting out various other gremlins) You guessed it - 5500rpm and 35kts, but bags of slip! (About 22% ) By this time I was running the numbers, weights etc through a plethora of prop-calculators and two (including the Mercury one, suggested that a Trophy Plus 23.4p was optimal prop, so as they don't do a .4 I searched on a 23p and found one 'as new, unused' for £200. More than I wanted to spend, but by this time the inner speed freak was convinced I could wring out another 4kts on the best achieved so far to get to the magical 40kts... I'd had various fuel issues and a trim problem, so it wasn't until early this year with fixed trim, cleaned carbs, new pump diaphragm and renewed impetus that I could test. Went down to Plymouth Sound with a friend who's a former powerboat racer and, shod with the 23p Trophy took her for a blast. Didn't quite expect the result we got, but (thankfully) with much more knowledgeable friend at the helm, we found that the bite was perhaps a tad too much for choppy water as the boat had a serious lean and wanted to corkscrew whenever we got the hull out! Not ideal for a family boat. Not wanting to start lifting engine etc and more serious tuning methods, I've (almost!) concluded that 35~36kts is enough! Interestingly, we did head up the Plym to the water-skiing area and took turns to sit in the back so we could move to balance out the 'list' and we did get 36.8kts on the GPS at 4600rpm. Shows there's more to go, but into the same overloaded engine situation that you have. I've also since leaned that the Laser II gives bow lift, whereas the Trophy Plus gives stern lift, so maybe need to test again without the tabs - or is that just an excuse to get more testing in? In short, you could spend a fortune trying different setups and first attempt may not give what you expect! You certainly appear to need to drop down in pitch in order that engine can reach it's potential and not be overloaded. I suspect as others suggested, previous owner calculated maximum speed rather than achieved it - at least not with that prop! It's easy to play with small boats, trying different setups etc but a 5 tonne vessel is presumably going to be quite expensive if you have to lift out too often! I wondered about more blades to help lift yours over the hump, but without knowing how much slip currently and an accurate idea of setup, dropping a pitch would seem the more viable starting point? You'd also need to drop even lower if you added a blade 16/17p perhaps?
(As for me, I'm looking out for a 20p or 21p Trophy Plus now - not too seriously, but looking all the same...
)Latestarter1
Well-Known Member
This is not going to be an expensive exercise, I am not talking about any cutting, any decent prop shop can hot graunch a couple of inches of pitch on or off for about £150. HOWEVER my recommendation of propeller size come with the caveat that your input data is 100% correct, however surely worth a punt to buy your way out of propellers anonymous.
Here is a thought, contact the builder and ask for a copy of the original installation review carried out by Cummins Diesel. Engine WILL have have had to reach rated speed on sea trials in order that warranty is signed off. The Cummins installation review also specifies the given prop size. This document is worth its weight in gold and copy should always be part of ships papers.
Re reading your posts let me put your mind at rest on the issue of engine speed and fuel consumption. Remember this is a diesel engine, throttle sets the engine speed not the power output. Look at a B 210 data sheet, engine has over 200 potential hp available right down to 2,000 rpm. Remember I said that a max waterline speed your propeller demand on 2.7 exponent is just over 140 hp. In the engine speed range of 2,000 to 2,600 rpm if you compare power demanded vs potential power there is a discrepancy of 60 to 70 hp where is that power going? The engine is not developing it, governor simply holds rpm providing fueling dependent on load demanded by the propeller.
Good luck
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Pugwash81
Member
Hi,
Did reserurrecting an old thread. Did a new prop sort this?
See the boat for sale and want a bit of info please from the owner.
Kind regards,
Matt
Did reserurrecting an old thread. Did a new prop sort this?
See the boat for sale and want a bit of info please from the owner.
Kind regards,
Matt
QBhoy
Well-Known Member
I think most are either optimistic or rely on dreamometers (boat spinny wheel or water pressure speedo)
Plenty up here on the Loch will tell you their 3.0 bayliner bowrider will do 50mph. Nonesense. Over 40 gps is a fast boat and achievable with decent hp on such a boat. Over 50 is a really quick boat with serious power. Over 60 is a total barrier that only a handful of boats will see outwith your bare bones racing hulls like ring and phantom. Even they only just manage a genuine 60 gps with a big v6.
I know all too well the challenge. I’ve been trying to nudge 70 for 3 years. Best to date is a freak 66.7mph stripped out. Normal good day would be 63/64gps. Of course the speedo will read silly about 70 odd, haha. Few thousand pounds on props etc later, I’ve given up. The increase in HP required to edge just a few mph extra at this level is rediculous. Without going full on yank on it with a supercharger, I’m kidding myself on !
Plenty up here on the Loch will tell you their 3.0 bayliner bowrider will do 50mph. Nonesense. Over 40 gps is a fast boat and achievable with decent hp on such a boat. Over 50 is a really quick boat with serious power. Over 60 is a total barrier that only a handful of boats will see outwith your bare bones racing hulls like ring and phantom. Even they only just manage a genuine 60 gps with a big v6.
I know all too well the challenge. I’ve been trying to nudge 70 for 3 years. Best to date is a freak 66.7mph stripped out. Normal good day would be 63/64gps. Of course the speedo will read silly about 70 odd, haha. Few thousand pounds on props etc later, I’ve given up. The increase in HP required to edge just a few mph extra at this level is rediculous. Without going full on yank on it with a supercharger, I’m kidding myself on !
