Mr.KingSpooled Posted March 16, 2012 Share Posted March 16, 2012 Hey raiders, I was just thinking about upgrading the power plant on my boat from the 20hp to a 30hp just to help it get out of the hole a little quicker n make my longer endurance runs on the George's a little faster. Only problem is my Stacer sea sprite 3.85 alloy is rated at 25hp max. At the moment the 20 is doing an ok job but for where I fish normally in the rivers and estuarys the water is really calm so flat knacker is the way I go except flat knacker with the 20 isnt all that fast especially if the boat is all geared up n I have a 2nd or 3rd person in the boat ! Also when I'm in the bay and I encounter some chop it gets really sluggish !! Once it gets up it moves but with chop u can't really hold it flat the floor so in turn makes the boat really slow through some decent chop until I get a calmer patch to let the boat get up to speed! Hence I want a 30hp just for that little big extra ooomph to get up and go! From how it handles now I don't see a problem in wacking 30 on the back, but I'm only new to boating so I dont wanna just go ahead n do it and then find out I've made things worse ! Handling,weight etc etc ! Any help on this would be much appreciated ! Cheers, Jeremy Link to comment Share on other sites More sharing options...
hughsnews Posted March 16, 2012 Share Posted March 16, 2012 Just remember I think they can sting you for having an engine larger than the one rated... Will the 30hp weigh a lot more and burn through fuel quicker(thus larger tank needed) and more weight in general?!!? Best of luck with the engine!! Link to comment Share on other sites More sharing options...
Mr.KingSpooled Posted March 16, 2012 Author Share Posted March 16, 2012 Yeah that's the thing, not sure on rules regulations n how it will affect the overall performance!! I'm sure some raiders would have gone through what I'm thinkin and know exactly how this would work ! Link to comment Share on other sites More sharing options...
Juggs Posted March 16, 2012 Share Posted March 16, 2012 dont put more hp then max on the back, its against the law to exceed the manufacturers compliance plate, and now a chargeable offense if caught remember in your licence test " your the skipper your responsible" "Registration of a vessel may be cancelled or suspended if the vessel has become unsafe" or unseaworthy (exceeded the compliance plate makes the vessel unseaworthy) look at the cubic capacity of the 20 versus the 25 yamaha 20 395 cc Recommended Max RPM 5500-6000 yamaha 25 395 cc Recommended Max RPM 5500-6000 same cc and rpm, so must be in the jetting and exhaust system or compression the 30 then jumps to 496cc find the 25 with the biggest cc as that is where torque comes from Link to comment Share on other sites More sharing options...
onearmedfisho Posted March 16, 2012 Share Posted March 16, 2012 Yeah that's the thing, not sure on rules regulations n how it will affect the overall performance!! I'm sure some raiders would have gone through what I'm thinkin and know exactly how this would work ! A new Merc 25hp weighs exactly the same as a new 30hp and im pretty sure your 20hp Mariner would be the same 51kgs... you can get fined but unlikely... Link to comment Share on other sites More sharing options...
daniel944 Posted March 16, 2012 Share Posted March 16, 2012 What rpm is your 20hp doing at WOT? You want to be getting close to 6000rpm with min load, if not put a smaller prop on the 20hp before buying a new motor. PS if you put a 30 on your boat then your asking for trouble. Link to comment Share on other sites More sharing options...
Fisherman36 Posted March 16, 2012 Share Posted March 16, 2012 You'll find that going more than the recommended HP will also void your insurance. I don't know about you, but if anything happens to my boat I want the insurance company to pay for it not me. Link to comment Share on other sites More sharing options...
DTROJAN Posted March 16, 2012 Share Posted March 16, 2012 Hey raiders, I was just thinking about upgrading the power plant on my boat from the 20hp to a 30hp just to help it get out of the hole a little quicker n make my longer endurance runs on the George's a little faster. Only problem is my Stacer sea sprite 3.85 alloy is rated at 25hp max. At the moment the 20 is doing an ok job but for where I fish normally in the rivers and estuarys the water is really calm so flat knacker is the way I go except flat knacker with the 20 isnt all that fast especially if the boat is all geared up n I have a 2nd or 3rd person in the boat ! Also when I'm in the bay and I encounter some chop it gets really sluggish !! Once it gets up it moves but with chop u can't really hold it flat the floor so in turn makes the boat really slow through some decent chop until I get a calmer patch to let the boat get up to speed! Hence I want a 30hp just for that little big extra ooomph to get up and go! From how it handles now I don't see a problem in wacking 30 on the back, but I'm only new to boating so I dont wanna just go ahead n do it and then find out I've made things worse ! Handling,weight etc etc ! Any help on this would be much appreciated ! Cheers, Jeremy You could always try installing a stingray type wing first if you don't already have one. I think it makes a huge difference and it's a cheap and easy thing to try first before forking out $$$ for a bigger motor. Link to comment Share on other sites More sharing options...
Testlab Posted March 16, 2012 Share Posted March 16, 2012 How old is the current engine? 80s, 90s or younger? Link to comment Share on other sites More sharing options...
Zdenk01 Posted March 16, 2012 Share Posted March 16, 2012 mate, you need to consider how much weight is in the boat aswell, maybe the prop pitch may be another option. I had a 15hp on my 3.60 tiny (which was very light) I had 2 props for it. The speed i got was unbelievable from one of them. On my own in a river id pass other boats @ WOT Id get some strange facial expressions. Like a few have already mentioned, you need to know what rpm @ WOT Huey may be the man to speak to. Mork calling Huey come in Huey cheers Zed Link to comment Share on other sites More sharing options...
Mr.KingSpooled Posted March 17, 2012 Author Share Posted March 17, 2012 The motor is a 94 Marine 20hp 2 stroke. So its not ancient but its not exactly new either. I think I might just look into a 25hp with bigger cc's as mentioned above. Sounds like the best plan plus wont get pinned for it either. Cheers for all the great info guys. Jeremy Link to comment Share on other sites More sharing options...
OzMacca Posted March 17, 2012 Share Posted March 17, 2012 Jeremy a lot of the older motors the hp was rated @ the flywheel. Most Outboard motors Now the hp is rated at the prop. I think if you were to update your motor to a newer 25hp I'm sure you will be happy and legal . Cheers Tommy Link to comment Share on other sites More sharing options...
Guest Aussie007 Posted March 17, 2012 Share Posted March 17, 2012 go a new 25hp tohatsu i ran a new 18hp tohatsu on a 3.75m ally craft with 3 adults in the boat it went the same speed as a single adult in the boat with a 20hp johnson with 1 person in the boat alone and the 18hp tohatsu was scarey at full throttle it was so fast some of the 20hp engines have the same powerhead as the 25hp version just different carby ask huey he will know u might be able to get away with it cheaply by just changing the carby from a 20hp to 25hp Link to comment Share on other sites More sharing options...
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