New engine for 4.2m SIB - 4stroke?

Ed the Duck · 13 July 2006, 17:47

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!

codprawn · 13 July 2006, 18:53

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.

rugrat · 13 July 2006, 21:16

how about the tohatsu 50hp TLDI or LPDI?
ive heard good things about these engines

fast fred · 13 July 2006, 21:55

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

toby.budd · 29 July 2006, 10:13

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

Poly · 29 July 2006, 11:18

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!

Ed the Duck · 05 August 2006, 10:02

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!

Ed the Duck · 07 August 2006, 12:16

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

tinker · 11 August 2006, 16:04

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

ian parkes · 11 August 2006, 22:57

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 .

codprawn · 12 August 2006, 02:14

Have you seen what happens to most 4 strokes when water gets into the air intake? Bent valves and conrods. I saw a 2 stroke outboard the other day merrily bubbling away under water until it stopped - they had it running again in 1/2 hour.

ian parkes · 12 August 2006, 10:05

Quote:

Originally Posted by codprawn

Have you seen what happens to most 4 strokes when water gets into the air intake? Bent valves and conrods. I saw a 2 stroke outboard the other day merrily bubbling away under water until it stopped - they had it running again in 1/2 hour.

Merily bubbling away underwater untill it stopped ?? get real and think . Both engines will damage due to hydraulic action of the water it just depends how fast the thing is going when it goes under . Any engine drawing a lung full of H2o at full chat is dead .

codprawn · 12 August 2006, 11:45

Quote:

Originally Posted by ian parkes

Merily bubbling away underwater untill it stopped ?? get real and think . Both engines will damage due to hydraulic action of the water it just depends how fast the thing is going when it goes under . Any engine drawing a lung full of H2o at full chat is dead .

Not so on 2 strokes because they have ports instead of valves. Granted the engine wasn't going flat out though - was probably just on tickover as the driver's foot was no longer on the throttle!!!

ian parkes · 12 August 2006, 14:32

Quote:

Originally Posted by codprawn

Not so on 2 strokes because they have ports instead of valves. Granted the engine wasn't going flat out though - was probably just on tickover as the driver's foot was no longer on the throttle!!!

The ports are the reason for the extra problems water gets to the Big ends little ends and main bearings then gets above the piston . Its all much harder to get out and does damage as the engine is starved of oil as you turn it to get it started .
Ports or valves damage still happens if its revving .

al40 · 16 August 2006, 23:11

Quote:

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

I've dunked a small 2s engine twice (both times running). 1st time boat tured over and engine got swamped - was running when it went under and ended up full of water.

2nd time I was wearing the kill chord and the engine bracket broke on my little Avon 9ft. Engine fell of the back, stopped because of kill chord and was left dangling by the secondary attachment (ie rope). Got it back to shore and it started. The inside of the cowling was pretty much dry as there was obviously an air bubble inside the cowling preventing any water to get in (air vent holes are on underside). I did drain the fuel and re-fill as there was water in the fuel tank.

I guess whether the engine gets flooded depends on many things - position of crank when it stops (whether water can get into cyl via exhaust port or whether exhaust valve is open on 4str), whether the engine is running when it goes under (I assume if the boat inverts, engine will stop due to kill chord).

4 strokes are notoriously fussy about positioning of the engine to prevent oil draining out (ie which side you lay them on if transporting with a car). After a capsize, it's likely the sump oil is everywhere so may be a bad idea to try and start them without a good check over first.

The RNLI do (or certainly did) mod's to their 2-strokes to make them start after a capsize...

BogMonster · 16 August 2006, 23:26

Quote:

Originally Posted by al40

4 strokes are notoriously fussy about positioning of the engine to prevent oil draining out (ie which side you lay them on if transporting with a car). After a capsize, it's likely the sump oil is everywhere so may be a bad idea to try and start them without a good check over first.

I only have experience with upside down vehicles but I would think that it would be OK as long as it was righted fairly quickly?

Vehicles usually are, the problems come when you leave them upside down for a long period (hours or even overnight) and the oil creeps past the piston rings etc, then you try to start it up and bang, hydraulic the engine due to the oil in the cylinders.

ian parkes · 16 August 2006, 23:34

there is so much talk of 4 strokes draining the oil out . If one had been rolled then it would be a good idea to check the oil on the dipstick . A 4stroke would need to be left on the wrong side for quite a while for a problem to occur .
A to make sure water hadn't got into the sump
B to make sure there was enough oil in it .

The entire contents of sump oil would be unlikely to find its way out of the engine , if it could it would all be pushed out while the motor was running .
If water entered through an open valve it can still only get above the piston ,
A the engine will iether not turn over due to hydraulic action of the water , in this case removing plugs etc will sort it out
B the water will be purged through the valves

If its any conselation , last year I made a mount for my canadian canoe and used a Honda 2.2 . My mate also got the same outfit . and he recently tested it for wet starting .

last week he told me he had capsized the canoe . The kill cord stopped the motor I guess , he said he drained the carb and it started easily . It was upside down for long enough for him to get to the bank of the river 5 mins I guess no oil was lost and no water got into the oil .

What modifications do the RNLI do to make an engine start easier after drowning ?

Poly · 17 August 2006, 11:12

Quote:

Originally Posted by ian parkes

What modifications do the RNLI do to make an engine start easier after drowning ?

Turbo diesel has explained it here in another thread before

ian parkes · 17 August 2006, 12:58

Quote:

Originally Posted by Polwart

Turbo diesel has explained it here in another thread before

Interesting stuff which also backs up my experience that a 2 stroke is a major problem to start when the crankcase has water in it . In fact many older 2 stroke off road bikes used to have a drain plug in the crankcase ,
Montesa and bultaco I think

Ed the Duck · 24 August 2006, 21:53

Thanks for the replies-

Will stick with what I know for now...

From experience, I can restart the 2 stroke Mariner after 5 minutes upside down in surf (without PIRS kit). Will wait to learn from other peoples experience of swamped 4 strokes and look forward to seeing which engine the RNLI specify to replace the Mariner 40hp 2 stroke on the D-Class ILB (SIB).

Thanks

Ed