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Old 13 July 2006, 13:47   #1
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Country: UK - England
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New engine for 4.2m SIB - 4stroke?

Looking for advice as to a good choice of replacement outboard for my Gemini GRX 420 (SIB cat like a zapcat with bow).

Am currently using a 40hp 2cyl 2 stroke short shaft Mariner. Quite a heavy motor (says 93kg on the leg) but can't fault it's reliability, robustness and ease of servicing (particularly after capsize). Like the grunt and acceleration of the 2 stroke in the surf, but once I start to head on longer passages, the noise and fuel consumption start to become a bit of a pain. Can't help thinking that the heavy 40hp may actually give a similar performance to the lighter mariner 30hp.
See on old posts that Toby Budd had the GRX with a 30hp - any one in touch with Toby or have experience of his old boat?


Anyone know of the lightest manual start 2 stroke and 4stroke in the 40-50hp range?

Any advice as to the liklihood of restarting a 4 stroke engine after capsize?

Such thing as a manual start direct injection?!?


Looking at doing some big distances with the boat next year far away from petrol stations. Would prefer not to go deaf and tow around a barge of fuel!
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Old 13 July 2006, 14:53   #2
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Most people swear by the Tohatsu - especially for ZapCat racing but they are prob stopping making the old tech 2 strokes.

Prob the lightest 4 stroke 40hp is the Yamaha - 72kgs or thereabouts. There was quite a long thread on this a while ago if you do some searching.
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Old 13 July 2006, 17:16   #3
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how about the tohatsu 50hp TLDI or LPDI?
ive heard good things about these engines
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Old 13 July 2006, 17:55   #4
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the TLDI 40 or 50hp works well on that style hull, with a 30hp it is some what underpowered when it gets bumpy. don't think the hull will perform even close
with a 4 stroker
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Old 29 July 2006, 06:13   #5
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Grx

Ed, I have just bought one of my two old GRXs back and have sold it to a mate who lives in Dawlish, Devon, great boats.

I was speaking with a friend the other day who has also owned a GRX as well as a Zapcat, we were talking about fuel consumption, we reakon the 50hp yam or tohatsu could use a full 25 litre tank in an hour dirving like full wack like a lunatic (As it is hard to drive a zap cat any other way), thats (Average 1 litre a mile ish) and that the new 250 hp 4/s burns about 1.3 lpm, not much more at the same sort of speed on a big rib, give or take, amazing really how far it's all come.

I was also running the 40 hp ex rnli ob on my first GRX, really great engine, bomb proof, capsized many times and allways started with loads of grunt. think you will find that when you go up to the yam or tohatsu 50 it jumps to 3 cyl and also an increase in weight, not sure about this but think that extra cylinder will cost in weight. I would say 40 is apmle unless your racing or carrying big loads.

if you are looking more at cruising i would def look to the 4s market 25-40 hp as you you should get incredible fuel consumption with such a light boat, i was looking at this for my boat and looked at the 25 4/s yamaha, it is 2 cyl in weighs only 37 kilos and i thought would be ideal for 20 kont cruising for 2 pax and gear, if you go up to the 30 or 40 yam 4/s you get into much more weight about 74 kilos i think with three cyl and power trim and tilt.

My plan was to go for the 2 cyl 25 for cruising and keep the 40 for stupid stuff in the surf.

Hope this helps,

Toby
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Old 29 July 2006, 07:18   #6
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Quote:
Originally Posted by Ed the Duck
Can't help thinking that the heavy 40hp may actually give a similar performance to the lighter mariner 30hp.
seems unlikely - to get the same speed you would need more revs so use more fuel.
Quote:
Any advice as to the liklihood of restarting a 4 stroke engine after capsize?
probably much harder than a 2 stroke. I have a little 2 HP 4 stroke and it really doesn't like being on the wrong side never mind upside down. Takes about 20 minutes "faffing about" changing / cleaning the plug turning over the engine with plug out etc. And that is with just 1 cylinder. Not something I would fancy afloat (I have no experience trying to restart a 2 stroke that has been capsized - so perhaps it is just as hard.

Turbo diesel recently posted on another thread about the post immersion start kits they (he works for Barrus) can supply for Mariner engines. Would be worth a search - but presumably its not cheap or they would be fitted as standard!
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Old 05 August 2006, 06:02   #7
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Quote:
Originally Posted by toby.budd
...
My plan was to go for the 2 cyl 25 for cruising and keep the 40 for stupid stuff in the surf.

Hope this helps,

Toby
Thanks for your replies...

Rapidly coming to the same conclusion. When running down sea in big surf I wouldn't want anything less than 40hp- for the more sedate days (when no chance of capsize) a 25hp 4s would be ideal.

20-22kts seems to be a good (sustainable and comfortable) cruise speed for the boat and I would hope to get it with 25hp. Will do some research and see how long a 4s 25-30hp engine will run on the 2x 25 litre tanks.

The 2 stroke is easy enough to resart after capsise (although have never managed it on the water though- when i've capsised I've waited to end up on the beach). Short of a sophisticated PIRs kit, I cant imagine a 4 stroke being so tolerant of such abuse!
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Old 07 August 2006, 08:16   #8
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Quote:
Originally Posted by rugrat
how about the tohatsu 50hp TLDI or LPDI?
ive heard good things about these engines
Done some web searches - TLDI needs a battery - no pull start model available. Have considered a battery box for vhf and nav lights etc, but wouldn't want to rely on electric starting in the surf. Do look like good engines though.

Will try and find a 30hp 4stroke to experiment with. Dont mind losing speed in return for range- In most conditions, 25kts in the grx feels as fast as a 28' deep v at 55kts. Definitely a case of crew failing before the boat does.

Ed
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Old 11 August 2006, 12:04   #9
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My mercury bigfoot 25 hp 4 stroke runs all day long at 3/4 throttle (18 mph) on one 25l fuel tank I would say about 0.5l a mile. full throttle is more thirsty but havent really run it that long at wide open throttle to give any figures. In any decent waves say 1m + high with a speed over 25mph it gets pretty hairy and could quite easily have chucked me out.
hope this helps
mark
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Old 11 August 2006, 18:57   #10
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Hi Ed I remember chatting ages back about sibs in surf . I know its smaller than you have but the little honda 3.8 I had then did about 50 miles on 8 litres with a honda 20 . It did about 20 knots flat out and cruised easy at 15 , but as you sat power was lacking in big waves and could have got me in trouble .

As for the starting after a drowning I hope i never find out in a boat , but I used to do a lot of off road biking , one day we drowned about 4 bikes in a river really bad , right under . Mine was the only 2 stroke and took forever to get going properly . The 4 strokes we just drained the carbs and tipped them up to empty the exhaust and away they went . I was amazed untill I thought about it , the 4 stroke only takes fuel/air in above the piston in one side out the other , the 2 stroke had sucked water into the crankcase and kept wettin the plug etc as it tried to pump out the water . Later that day it siezed on me , i think due to water washing the oil off the bearings and also causing a problem with the auto lube .
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