GPS speed or dream dial I wonder Brett ? If it's on GPS it is well quick for a rig that size.Originally Posted by brett62
Either way it gives you something to aim for with the new engine hey Lol
GPS speed or dream dial I wonder Brett ? If it's on GPS it is well quick for a rig that size.
Either way it gives you something to aim for with the new engine hey Lol
That something's wrong with your GPS, speedo or glasses prescription Dave. Was it a GPS speed, or speedo? And was it knots or mph? Even if mph, still seems high.
That speed with a 20p prop at 5000rpm and 2.0 ratio leg is 'impossible' I reckon Dave.
Mid to high 30's maybe even 40 'knots' max at a guess without actually crunching the theoretical speed calcs.
And 55 knots.... nah.
Cheers
Brendon
nice
WOT at 5000 rpm is spot on
runs good and sounds even better
if you can cruise at 3400-3700 and hold on plain it is all sweet
Just watched the video Dave, that hole shot is pretty good for a 7m Whitley that would be heavier than your 2t I reckon.
What is the max REC Rpm for that donk?
Theoretical speed is 5000 x 20" / (2.0 x 3.2808 x 200 x 1.852) = 41.1kn.
Allow 5% slip (might be more in reality) and your speed will actually be around 39kn....
To get to 50kn you would need around 500hp +/- Dave.
Cheers
Brendon
Scott re thinking the re-power after those figures. LOL
Brendon the weight of my boat when it hits the water is 3 ton and that's without people. You would certainly want serious HP to get to 50-55 knots. Don't think I would like the fuel bill either.
Dave's video shows it doing everything good.
Morning Guys!.
So a little more testing has confirmed what you chaps are all saying. Sorry if i confused anyone.
I installed an app on my iphone to show GPS speed, and indeed the speedo on the boat seems to be way out!. Is this a common thing??
Brendon your calcs are very accurate.
With the 22P props on the boat at about 4900 RPM WOT, i managed to top out at about 77km/h.
If i plug this into your calculation, allow 5% slip and convert to knots, i get 44.3 knots (which equals 78km/h). So, if i put my 20P props back on (which is my preferred), i should get a max theoretical speed of roughly 73km/h (assuming i reach 5000rpm).
Forgive my ignorrance (im no mathematician!), would you mind helping my understand that calculation?
5000 = RPM
20" = Prop pitch
2.0 = Assume this is outdrive ratio
1.852 = Conversion to knots
3.2808 = is this some sort of feet/meters conversion?
200 = This is confusing me.
The real test will now be to see how it performs with full gear and another family on it.
Im also now thinking id like to put a slightly larger camshaft in it
Dave
It's a pretty regular occurrence. Hence the dream dial reference. With your RPM's at take off, the thing to take into account is that marine engines, unlike cars, run only one gear ratio (no changing gears as you accelerate) so realistically it's like taking off from the lights in 4th to a point.
Howdy Brett,
Just wanting to come back to your above comment if i can (and get input from any other board members).
The thing that is still bubbling away inside my is how you manage to get 4000 RPM on takeoff??. This is now the single thing thats making me "hang on" to this issue. What motor do you currently have?. Yesterday's testing certainly shows that the boat can get up on the plane, and hit top RPM, however this was a very controlled test.
If i were to throw my usual gear onboard along with my three small kids and wife, full water, full fuel, and our family friends (2 adults and 2 kids), i suspect i will have the same issue i always do which is still 2900 RPM and a loooooong time out of the hole (to the extent i need to distribute weight to the front). Only testing will tell - but im still hanging onto your 4000 rpm on takeoff.
@scottar - understand exactly what you are saying. And certainly understand the concept of the ratio's etc. My issues is that i just assumed id be able to pull more than 2900 RPM on takeoff. Perhaps im just expecting too much.!!!!
Christmas tomorrow people! - anyone got any new boaty toys coming?
Dave
Brett - was yours a duo prop set up like Dave's is ? Dave - did you ever look further into a foil (if my memory serves me correctly you didn't have one) ?
full conversion calculation the way I did it was; 5000 x 20” x 60min / (2 x 12 x 3.2808 x 1852) = knots
Grouping/reducing whole number conversion factors we get; 60 / (12 x 1852) = 1 / (200 x 1.852) … so that's where the 200 comes from. Just makes the equation smaller/easier and less typing
PS. Forget about the rpm on take off Dave, this doesn't mean much so long as she is getting up nicely - which your's is. You prob have near twice the blade area Brett does = bugger-all slip at take off = low revs in comparison while the torque is overcoming the "hump load" with minimal slip.
Yours is jumping on the plane now, all good! Check against max REC WOT, check again fully loaded. Maybe the 22p might be fine as a day prop unless really heavily loaded.
Merry Christmas
Cheers
Brendon
Merry Christmas Dave.Howdy Brett,
Just wanting to come back to your above comment if i can (and get input from any other board members).
The thing that is still bubbling away inside my is how you manage to get 4000 RPM on takeoff??. This is now the single thing thats making me "hang on" to this issue. What motor do you currently have?. Yesterday's testing certainly shows that the boat can get up on the plane, and hit top RPM, however this was a very controlled test.
If i were to throw my usual gear onboard along with my three small kids and wife, full water, full fuel, and our family friends (2 adults and 2 kids), i suspect i will have the same issue i always do which is still 2900 RPM and a loooooong time out of the hole (to the extent i need to distribute weight to the front). Only testing will tell - but im still hanging onto your 4000 rpm on takeoff.
@scottar - understand exactly what you are saying. And certainly understand the concept of the ratio's etc. My issues is that i just assumed id be able to pull more than 2900 RPM on takeoff. Perhaps im just expecting too much.!!!!
Christmas tomorrow people! - anyone got any new boaty toys coming?
Dave
Mate I am running a single four blade prop on a Bravo 1 drive. The four blade is much better for getting on the plane than the 3 blade which is now the spare I carry. The motor is 5.7 L 300hp carby engine.
I purchased the boat secondhand and the previous owner had just replaced the engine and did say that he replaced with a performance engine which has a few extra upgrades such as cams, rockers and bearings. The motor is now out of the boat and was surprised as was Jim that she is a real 350 chev engine. Looking at your video and comparing to how quick I get out off the hole you are not far from what I do. The difference when fully loaded with my set up is very little. I don't have your top speed but have better low down performance. Remember you are over 3 ton in this boat with people added. They are not going to jump out on the plane like a ski boat. Also you should be doing your test with the boat in the configuration that you would normally run at. Put the weight in the boat and then do your testing and prop performance as things will change. I have set the boat up for the best cruise performance and also making sure I get to that recommended WOT RPM so the engine is not loading. If I wasn't replacing the motor with a diesel I would have played some more with props but Jim will have to start the science experiment again and I will also be using a Bravo 3 leg. Gear box ratios is something that comes into play also.
All the best and interested on your test results once you've completed your science experiment.
Brett
Hi guys.
For the first time in many years I'm lying here in bed awake before the kids, so thought I would take a moment to close this out.
Scottar - I did look into a foul (and in fact bought one off eBay that didn't fit the B3). I'm having trouble finding one for the B3??
Brendon - thanks for that, and I think you are right. It might be time to put this takeoff rpm thing to bed. I now have a better understanding as to why Brett might be getting higher rpm than me takeoff with peg gaps a little more slippage. Learn something new every day!!
I'm going to get my 20p props cleaned up and balanced. They are a little rough around the edges so that may also just tidy things up a little.
Brett - thanks for that. I don't suppose you have any detail of the cam in your motor? That's something I'm toying with. I have a pretty full auto workshop at my place and love rebuilding engines in my spare time. I'm planning on freshening up the Mercruiser over winter and a cam is on the cards. Just a small one. From what I can gather they are a pretty standard chev part....and theta single cam engine so not too pricey to do.
Did you ever get around to putting it on a weigh bridge?
Merry Christmas all. And sincerely thanks for all your help.
Dave
Sent from my iPhone using Tapatalk
Dave I will pulling the top of the motor very soon and I will see what it is running. Yes I did put the boat over the weigh bridge and the boat came in at 2.8 ton with no batteries, not full of fuel and water. It will be 3 ton easy when it hits the water. This is the real weight of our boats. I carry 320 litres of fuel and 150 litres of water. I estimated I had about 150 litres of fuel in the boat when I weighed it. Dave they are not light and that is good in my opinion as they push through the water and are not bouncing around kicking the shit out of ones self. Once again Dave your video is showing her running well. If you want more horse power and you are going to strip it down that will be the time to pimp the motor for sure. Having played with my boat I have found that the hull really likes to cruise at 23 -25 knots. That will be my goal with the re-power and hope I can get around that.
No problems Dave. Been awake early too, but unfortunately that's from work issue's and not boating 'things' - they're the problems we don't mind losing sleep over aren't they??
Merry Christmas to you guys, and all Ausfishers too!
Brett,
your new diesel will be great I am sure, 240hp 4cyl from memory? Don't be too concerned about the drop in HP (in comparison to petrol - especially in relation to cruise speed), as the mountains of torque is what provides the thrust you need. Top end speed will most likely drop, but you will love the economy and diesel grunt!
Although they were heavy dinosaurs in comparison to today's oilers, was involved with many a boat conversion to diesel in the 80's with my late father's business in PNG.
The improvements to the Volvo 30 and 40 series diesels (4 & 6cyl), and the release of the DuoProp legs in 85 led to many people jumping from petrol to diesel - coupled with the big trips/miles and hours the boats would do, increased reliability and the cheap cost of diesel in comparison (at that time).
Common boats for the single 6cyl variants (430kg plus leg from memory) were the 25 Bertie's & sister Nova & 23 & 24 Huntsman's (flybridge models), 23 & 24 Fjords (and some others who's brands escape me ATM - but most bigger and heavier than your Whittley .
HP was initially 134, then 155 with aftercooler, 165 with D/prop and then 200,. Wasn't involved after this when Volvo added superchargers and the HP went up and up.
The addition of the DP to the 165 made definite improvement to low speed manoeuvrability, faster cruise, better economy and slightly faster top end too from memory - but they were still a bit slow when loaded with lots of fuel for big trips etc (we are talking days/weeks, 100's of nm's, if not more, with prearranged fuel dumps etc, another reason for diesel as the local villagers outboards didn't run too well on diesel
It was the 200 DP that really provided improvements, and 'zip' ... but would still be considered slow by today's standards. 19-23kn cruise (@ approx 20-30 L/h from memory, depending on boat and loading ... but it was a long time ago...
Your 4cyl 240hp will go great
Cheers & Merry Xmas
Brendon
Permatrim have a model specific to the B3 listed on their website if you can't find one elsewhere. I ended up with one of these on my motor ( The version to suit an E-Tec) - seems to work - cost about $300. They are a bit different to a lot of the plastic type foils in that they rely entirely on the angle of the outdrive to set the amount of lift (no downturned surfaces) but against the SE Sport that I also tried, it didn't generate anywhere near the same amount of drag. You could if you have the time and inclination fabricate one yourself.
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