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18' Outrage prop or engine issues
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| tootles |
Posted on 05/17/12 - 10:12 AM
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I have a new yahama 150 hpdi 2 stroke engine on a 1988 18.6 boston whaler outrage. I can not get the engine to hold rpm between 2000 and 2900. top end is 5800 rpm and otherwise the engine runs fine. with the 17 pitch prop i kinow i am a little under proped but is it normal that under propping won't allow the engine to hold a certain rpm. The boat jumps out of the hole and settles at 3100 or so . if you pull back on the throdle to say 2800 it holds for a minute AND then slowly drops the rpm to 2000. this makes it impossible to run rough water off a plane. The mechanic says i need a 21 pitch prop , it just doesn't make sence to me. Are any other 18.6 owners having this problem help!!!
Edited by Joe Kriz on 05/17/12 - 6:07 PM |
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| tedious |
Posted on 05/17/12 - 10:49 AM
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The behavior you describe seems perfectly normal to me. You need to be over the hump to get on plane, and then if you back off too far, it's going to drop off a plane. That's the way planing boats work.
It sounds like you're a little underpropped as the WOT range is 4500-5500, but if anything, that should help you hold a plane at lower speeds. At most I'd go to a 19-pitch, which should bring you to around 5500.
If you really, really need to be planing at lower RPM, try moving some weight forward in the boat, or adding trim tabs.
Tim
Edited by tedious on 05/17/12 - 10:53 AM |
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| Joe Kriz |
Posted on 05/17/12 - 11:07 AM
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When you say new engine, what year is this motor?
I don't see where Yamaha shows a 2012 150 HPDI with a 25 inch shaft for your boat... unless I'm missing something...
http://www.yamahaoutboards.com/outboa...ection-nav
See this list of current new motors available for an Outrage 18'....
http://www.whalercentral.com/articles...ticle_id=6
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| Phil T |
Posted on 05/17/12 - 11:21 AM
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At low speed up to 20mph, the hull is in the water, pushing it aside (displacing) the water. Above that, the hull is riding on top (planing) of the water.
As you go faster, the boat squats and creates a wave in front of it. To plane, the boat has to accelerate up and over the wave.
The speed you mention reads as just slow enough to come off plane and on the steep side of the displacement wave. No outboard motor likes that transition zone.
1992 Outrage 17 I
2019 E-TEC 90, Viper 17 2+
2018 Load Rite Elite 18280096VT |
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| Whaler27 |
Posted on 05/17/12 - 11:59 AM
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You need a 19 inch pitch propeller. If the motor can spin to 5800, the motor is underloaded.
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| tootles |
Posted on 05/17/12 - 12:57 PM
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Thanks All. I am not trying to hold a plane as that speed is too fast in seas. The engine is new old stock 2005 odel 150 yamaha hpdi. I have basically the same engine but 200 hp on a 1988 20' outrage and have no trouble riding bow high at a reduced rpm when wave height or weather dictates. THe 18.6 is a smaller and lighter boat, but even with a 17 pitch prop I cant run at any rpm between 2000 AND 3000 RPM regardless of the speed. I am told that this is a result of the prop being only 17 pitch and that I should get a 21 pitch prop. I will try some different props this weekend but it still doesnt make sence to me, I am looking to find someone with similar issues with this poarticular whaler. Years ago my fishing buddy had the same boat with a 1988 evenrude 150 and it was great, ran big waves great at a fast plowing speed
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| dreilly |
Posted on 05/17/12 - 4:00 PM
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I'm running a 19" prop on my Yamaha 150 2 Stroke V-Max and am not having the troubles that you describe.
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| Phil T |
Posted on 05/17/12 - 5:50 PM
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Pull the prop to identify the make, model and size of the prop. Not all 17" props are the same. As Tom Clark has posted, there are some that do well on your hull with that specific motor/gear ratio and others that are "junk".
It important that everyone who talks about a prop includes the size ( x by x) and the brand, otherwise we have no idea what prop you are talking about.
Blade design is not standard across brands and a prop from one brand will not perform exactly the same as a different brand in the same exact size.
1992 Outrage 17 I
2019 E-TEC 90, Viper 17 2+
2018 Load Rite Elite 18280096VT |
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| tedious |
Posted on 05/18/12 - 5:32 AM
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tootles wrote:
Thanks All. I am not trying to hold a plane as that speed is too fast in seas. The engine is new old stock 2005 odel 150 yamaha hpdi. I have basically the same engine but 200 hp on a 1988 20' outrage and have no trouble riding bow high at a reduced rpm when wave height or weather dictates. THe 18.6 is a smaller and lighter boat, but even with a 17 pitch prop I cant run at any rpm between 2000 AND 3000 RPM regardless of the speed. I am told that this is a result of the prop being only 17 pitch and that I should get a 21 pitch prop. I will try some different props this weekend but it still doesnt make sence to me, I am looking to find someone with similar issues with this poarticular whaler. Years ago my fishing buddy had the same boat with a 1988 evenrude 150 and it was great, ran big waves great at a fast plowing speed
Thanks for the clarification that you're looking to plow along, bow high. As another poster has mentioned, motors don't like to do that, but I understand you feel that's the best choice for particular weather conditions. My guess is that the speed range you're looking to be in corresponds to a low spot in the power curve of that particular motor. I looked around for a published power curve, but couldn't find one. The Yamaha performance bulletins all show a big step in the RPM / speed curve between 2 and 3K - similar experience to yours, I'll bet.
The issue is that at 3K, you don't have quite enough power to stay full up on plane, so you start to drop off. This increases drag and reduces your RPM, which takes you to an even lower point on the power curve, and the cycle repeats until you're down at 2K, off plane, and going slow but burning a whole lot of fuel and putting a lot of strain on the motor.
The reason going to a 21 pitch makes no sense to you is that it would make no sense to anyone - if anything, it will make your problem worse by bringing you to a lower point on the power curve earlier. I'd be thinking about going to a different mechanic 'cause this one seems a bit confused. If anything, you should be going to a lower pitch to get yourself up on the power curve at a lower RPM, but that of course will limit you at the high end.
The bottom line is that the behavior you're seeing is just the way it is, but if you have access to a variety of props, you'll at least be able to make the best of the situation. I'd still vote for moving weight forward and especially adding trim tabs if you want the best control possible.
By the way, my 15 has very much the same characteristics - doesn't like to run in that middle area. Nothing changed when I went from a 25 year old 2-stroke to a modern 4-stroke - that's why I say this is normal.
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| Derwd24 |
Posted on 05/18/12 - 7:55 AM
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When we got our new Etec, the dealer rigged it with a Raker prop and the boat performed very similar to what you're experiencing. Tom recommended a different prop, less swept design with more stern lift capability, and we also raised the engine on the transom. Made a world of difference in the performance of the boat, most notably in that RPM range.
As Phil suggests, start by identifying which prop you have on there now.
Edited by Derwd24 on 05/18/12 - 8:08 AM
Dave - 1983 Outrage 22 |
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| mtown |
Posted on 05/18/12 - 2:00 PM
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Not sure this helps but I had a 115 yamaha 2-stroke on my 1985 18' outrage and the prop was 12 5/8x21 stainless.
That was as rigged by a Whaler dealer, as a friend bought the boat new with that setup. I have since repowered, but the prop and motor were fine for many seasons. I just recently gave the prop to someone else for a Montauk, and am hoping it works for that. I tend to agree with the settling off plane comments above.
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| tootles |
Posted on 05/18/12 - 2:40 PM
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thankyou everyone, I will post my results when I start trying different props
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