Rob Posted March 26, 2009 Report Share Posted March 26, 2009 Hey chaps, For those who dont know I have a 15.5ft open light weight (300kg hull) with a 50hp 4 stroke Yamaha circa 2003\2004. I am having problems hitting my max revs \ power. The Yam is supposed to run at 5500 for max power (50hp@5500rpm), but I can only get it to run at 5000rpm, occasionally 5100rpm (Load = me with 35 litres of fuel, few fishing bits, 15kgs of anchors). This will get me to 28knots and that is fast enough for me!! But am I missing out on running at the max power point of 5500rpm? Am I missing out on potential fuel consumption? When running fast I do find if I play with the trim I hear the exhaust \ prop coimg out the water, feels like the prop is loosing grip, not sure if this is correct? I do run a pair of 40lb smar tabs and have set them to a low setting, should I go lower on the smart tabs? I can rev the engine out of gear to 6000rpm no probs (6000 is max revs). Can anyone help? Do I need a slightly smaller or bigger pitched prop? Current prop = 10 1/2" x 13" pitch Thanks Rob Quote Link to comment Share on other sites More sharing options...
Coddy Posted March 26, 2009 Report Share Posted March 26, 2009 Hi Rob For every 1" less pitch you should get about 200 extra revs If you trim out too far the prop will start cavitating, this means it will loose grip in the water and it could also damage the prop. This can happen in a following sea or on tight turns as well. Are you sure your prop is 10.5" Diam and not 13"? As it would seem a very small prop for your engine. Might be worth getting the prop checked out anyway and they may be able to reduce the pitch at the same time which would keep the costs down. Coddy Quote Link to comment Share on other sites More sharing options...
Paul J Posted March 26, 2009 Report Share Posted March 26, 2009 Hopefully the guys at propsol will offer some advice they are forum Members so send them a PM PJ Quote Link to comment Share on other sites More sharing options...
duncan Posted March 27, 2009 Report Share Posted March 27, 2009 For those who dont know I have a 15.5ft open light weight (300kg hull) with a 50hp 4 stroke Yamaha circa 2003\2004. I am having problems hitting my max revs \ power. The Yam is supposed to run at 5500 for max power (50hp@5500rpm), but I can only get it to run at 5000rpm, occasionally 5100rpm (Load = me with 35 litres of fuel, few fishing bits, 15kgs of anchors). This will get me to 28knots and that is fast enough for me!! But am I missing out on running at the max power point of 5500rpm? Am I missing out on potential fuel consumption? When running fast I do find if I play with the trim I hear the exhaust \ prop coimg out the water, feels like the prop is loosing grip, not sure if this is correct? Normal - you will also experience a little prop steer when trimmed to far in or out (the other way). Ideally the combination of weight loading in the boat, dynmic lift from the hull and whatever the tabs are doing should all come together with the propshaft exactly horizontal - here you have neutral steering and all the prop's drive is directed to forwards motion ie it's optimum effiecency. I do run a pair of 40lb smar tabs and have set them to a low setting, should I go lower on the smart tabs? They should be set so that they retract fully once the hull has reached it's dynamic balance - probably about 15 knots. They shouldn't be involved at all at the sort of engine/hull speeds you are raising. I can rev the engine out of gear to 6000rpm no probs (6000 is max revs). This doesn't actually confirm that it's actually producing it's normal power at this range but it's a good starting point. Can anyone help? Do I need a slightly smaller or bigger pitched prop? Given that you are only getting 5100 when pretty much at minimum loading I would certainly go to a lower pitched prop. On the face of it I would definitely loose 2". This should make the whole package a little more responsive with just you and probably give you your current performance when you have another fisherman and his gear on board plus another 25litres of fuel/tank. Quote Link to comment Share on other sites More sharing options...
Wedger Posted March 27, 2009 Report Share Posted March 27, 2009 Not wanting to hijack this one guys but whilst the prop guru is on form........... Duncan. I've just bought a second hand 290 DPE drive and sheild for Otter - the type sold originally with the AD31 130hp Volvo that I have. The hope is that with the extra efficiency I can make best use of the power where currently I am boarderline in the get-up-and-go stakes. Q. Proping. Where can I get a reliable prop calc for my setup? 130 HP turbo-diesel 19.5 ft waterline 21 OAL 2.4 tons (inc two fat bodies and a livebait tank) I'm not certain of the ratio yet but this I can checked tomorrow, however it came from a 21 footer with the same engine so here hoping! Just wondered if you had the info or an idea of what I need. Cheer T Quote Link to comment Share on other sites More sharing options...
Rob Posted March 27, 2009 Author Report Share Posted March 27, 2009 Dave - yes my prop is that small! 13" props are found on the High Thrust version of my motor. I think a 12" will fit though. Duncan - thanks for the info - I think I will try and smaller pitch. I can get a 10 7/8" x 11 or 12" x 10.5 - would there be much of a difference between these two? Thanks again for the advice. Yes Trev you have hijacked my thread but a I am fighting back!!! Rob Quote Link to comment Share on other sites More sharing options...
Coddy Posted March 27, 2009 Report Share Posted March 27, 2009 Rob/Trev Try this free calc from this web site http://www.castlemarine.co.uk/ Just enter all your data and it should come up with a good starting point. Coddy Quote Link to comment Share on other sites More sharing options...
Rob Posted March 27, 2009 Author Report Share Posted March 27, 2009 Cheers Dave - I have used the calculator and found a really good Yamaha document which shows various Yam engines on a huge array of boats, giving top speed, revs, and prop size. All in all, it looks like the prop is correct so I am thinking that maybe it is a simple as the cables have streched and need adjustment - I have not touched them in 2 years! And when running at 5100 my throttle is as far forward as it will go so maybe I will look at that before spending Quote Link to comment Share on other sites More sharing options...
britboard Posted March 28, 2009 Report Share Posted March 28, 2009 Rob if you want i can plug into your engine, as i have a Yamaha diagnostic system and tell you if anything is not working as it should do. The rev range on that engine is between 5k to 6k but the recommendation is to get it running into the upper half of the rev range in order to get the best out of the engine and to put in the best area for differing load conditions etc. I would be tempted to make sure its all working right and get the propping to give about 5750rpm with a light load onboard. If the charts you are looking at are the Yamaha US boat/engine tests IGNORE them as they are a mile off as most of the boaters in the US are only interested in going fast it seems and overpitch their boats to sqeeze as much speed as possible for the tests. My boat was propped to run at 5200rpm when i got it and it felt like it was dragging a large weight until it got going due to being overpitched now i have got it propped right it leaps onto plane, feels much lighter and responsive and burns 2 galls an hour less in fuel. Simon L Quote Link to comment Share on other sites More sharing options...
duncan Posted March 28, 2009 Report Share Posted March 28, 2009 Cheers Dave - I have used the calculator and found a really good Yamaha document which shows various Yam engines on a huge array of boats, giving top speed, revs, and prop size. All in all, it looks like the prop is correct so I am thinking that maybe it is a simple as the cables have streched and need adjustment - I have not touched them in 2 years! And when running at 5100 my throttle is as far forward as it will go so maybe I will look at that before spending Quote Link to comment Share on other sites More sharing options...
duncan Posted March 28, 2009 Report Share Posted March 28, 2009 Not wanting to hijack this one guys but whilst the prop guru is on form........... Duncan. I've just bought a second hand 290 DPE drive and sheild for Otter - the type sold originally with the AD31 130hp Volvo that I have. The hope is that with the extra efficiency I can make best use of the power where currently I am boarderline in the get-up-and-go stakes. Q. Proping. Where can I get a reliable prop calc for my setup? 130 HP turbo-diesel 19.5 ft waterline 21 OAL 2.4 tons (inc two fat bodies and a livebait tank) I'm not certain of the ratio yet but this I can checked tomorrow, however it came from a 21 footer with the same engine so here hoping! Just wondered if you had the info or an idea of what I need. Cheer T the most obvious idea is to get rid of the live bait tank........ seriously though you are going to have to establish the gear ratio first, and go from there. I suspect that your primary concern will be getting the pitch just low enough for the engine revs to be able to bring in the turbo before the hull speed hits the hump. The problem with with DPs are that they are too damm efficient and don't create enough slip otherwise. Having had the experiences with Phaeton on this I despair at times. Right now you should certainly have your fingers crossed re the gear ration but I agree your analysis that given the donor you are probably 'on the safe side' and should be able to get an effective combination sorted out for your boat. Quote Link to comment Share on other sites More sharing options...
Coddy Posted March 28, 2009 Report Share Posted March 28, 2009 Hi Trev Try this site for identification of your leg http://www.marinepartsexpress.com/vp_engine_finder.htm Looking at this I would suggest you have a one of two ratios, 1.95:1 or 2.30:1 also worth noting that the oil required is SAE90 Coddy Quote Link to comment Share on other sites More sharing options...
Rob Posted March 28, 2009 Author Report Share Posted March 28, 2009 Thanks Simon but mine is the 4 cylinder 4 carb version, pre EFI so I am not sure there is a diagnostic port - if you think differently then that would be great !! Duncan, Thanks for the advice - I think I will check the cables, as you said it's an easy on the drive test. Maybe a stripped down kit \ weight test drive with a lightweight driver is in order! PJ - when are you back up and running????? Thanks again Rob Quote Link to comment Share on other sites More sharing options...
Rob Posted August 2, 2011 Author Report Share Posted August 2, 2011 Well gents - I had dropped down to a 10 7/8" x 11 prop from 10 1/2" x 13" and have gained from 28 to 29 knts! My Revs are up to 5900 rpm were it was 5100 before and max power is @ 5500. The testing was done on Friday and I had 50 litres of baitwell water and a coolbox of fish! So a remarkable improvement, just need to run through my GHP fuel chart to see if it has changed. Thanks Dave and Duncan for the advice! p.s. didn't touch the cables as she could get max revs on the drive!! Rob Quote Link to comment Share on other sites More sharing options...
plaicemat Posted August 2, 2011 Report Share Posted August 2, 2011 Well gents - I had dropped down to a 10 7/8" x 11 prop from 10 1/2" x 13" and have gained from 28 to 29 knts! So a remarkable improvement, just need to run through my GHP fuel chart to see if it has changed.Rob So, assuming you were getting circa 25 knots, you are now getting circa 53/54 knots. Bloody impressive for just a change of prop, I must look into this. Terry. Quote Link to comment Share on other sites More sharing options...
Rob Posted August 2, 2011 Author Report Share Posted August 2, 2011 Nice one Terry! JoJo is now just a blip on the horizon, an Exoset if you will!!!! In fact she was doing around 55knts over the River Hamble, on the M27! Quote Link to comment Share on other sites More sharing options...
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