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Which fourstorke outboard and how much HP for a 2 ton Yacht?


Zozza

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I have a 2500kg boat and run a 9.9hp 4 stroke Yammy with the high thrust prop when cruising, it works magnificently. I do swap to old 8hp 2 stroke for the racing season. The 8hp does OK but would struggle into a big breeze/tide/waves or combo of. 9 out of 10 times the 8hp is more than enough.... but be warned it has performance figures of 0 to 5 kts in 15mins. 5kts to 0 takes about a nautical mile. The props are tiny so it has bugger all reverse or stopping in a hurry power.

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the yamaha hi thrust 4 stroke ten horse are great , quiet, economical, and heaps of push in forward and stopping power in reverse due to the big prop and reduction gearbox. I have had quite a few of them, from as far back as 1980.s and they have all been awesome. If you paid the money for a new or a good used one and looked after it it will be good for many years. The 8 hp will be just as good but probably not a lot cheaper. You can plan on 2 litres an hour for fuel at less than full throttle, I have had them on cats of around 4 ton and half throttle with one motor was about 5 knots. Flat out with 2 motors near 9 knots.Not sure how big your 2 ton keeler is but I had one on a 26 ft trailer sailer which would have been about 2 ton and it was heaps of power, would do 6 knots at probably 1.5 l/hr and half throttle or less. You could perhaps push your boat fine with a 5 horse but you won,t get one with the big prop that you need to stop you in reverse and push you into a strong wind and chop. Honda and others make good 4 strokes too but I think Yamaha has been generally accepted as the best for pushing a displacement boat because of the prop and gearbox design, and they have been doing it for a long time.

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Will be used mainly to just get in and out of marina.

 

Thanks in advance for anyones input.

 

 

Why not go ELECTRIC??

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Have a 2400kg yacht and use a Honda 8hp, after scanning all the available units picked Honda because of its gear ratio and torque, very happy apart from the weight (long shaft). P.S. I do the miles race weekly and cruise the bay each year from Auckland. The economy is excellent half of the previous 9.8hp two stroke and only dropped about 0.25 knot top speed in calm water, the rest of the time is quieter smoother and charges the battery.

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Yacht is 2 tonne. Have 15hp 4 stroke Honda mounted on 'rise and fall' in wet box. Heaps of grunt and does less that 3 litres per hour when runniing at 5.5knots. I chose the 15 as it has a 12 amp altenator and an electric start. Morse controls take care of the throttle and gears. I have also mounted a 90mm bilge blower to ensure that it gets plenty of air in the box. We get 7knots flat out!!

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Will be used mainly to just get in and out of marina.

 

Thanks in advance for anyones input.

 

 

Why not go ELECTRIC??

 

 

Ah, yes I have investigated this. if you mean Torqeedo. But I would have to import one direct myself as the NZ retailers of these electric outboards mark them up almost double the USA price. Even with duty from Mr NZ Customs they would still be a lot cheaper to import yourself.

 

I actually wonder about other bits of boat gear too--while our dollar has dropped a bit it is still strong and I reckon other bits of boaty gear could also be bought cheaper from someplace like 'Westmarine' than the sometimes obscene (not all the time) markup Kiwi chandlers and marine retailers whack onto certain items.

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Yacht is 2 tonne. Have 15hp 4 stroke Honda mounted on 'rise and fall' in wet box. Heaps of grunt and does less that 3 litres per hour when runniing at 5.5knots. I chose the 15 as it has a 12 amp altenator and an electric start. Morse controls take care of the throttle and gears. I have also mounted a 90mm bilge blower to ensure that it gets plenty of air in the box. We get 7knots flat out!!

 

15 hp? Yee gods. I was wondering if could get a way with a 4hp over a 5hp.

Still, thanks for your input and that sounds like an interesting set up but would not suit my boat and type of sailing.

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I have a 1.5 ton trailer yacht and have used both a Yamaha 9.9 four stroke and a Yamaha 8hp 2 stroke.

To be honest I prefer the 8hp 2 stroke. Its light, grunty and has a charge circuit.

The 8hp is around 36kg vs about 45kg for the 9.9 4 stroke. The power is similar but the 2 stroke uses more gas which isn't really an issue as we use the engine very little even when cruising.

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I have heard a variety of guidelines regarding outboard motor size, such as 5hp for every tonne of displacement. Or 1 hp for every 4 feet of length (cant remember if waterline or overall length).

 

One issue with using a small outboard as an axillary on a displacement yacht is that the blade pitch on a standard prop will be too great. To allow the motor to reach its designed revs a lower pitch prop is needed. Otherwise its a bit like being stuck in high gear in a car while towing a heavy load. A lower pitch prop is a bit like changing down gears. But the only way to get the best out of an outboard is to measure the revs while having the throttle wide open in good conditions, if the revs are not approaching the recommended high limit then a lower pitch prop should help.

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15 hp? Yee gods. I was wondering if could get a way with a 4hp over a 5hp.

Still, thanks for your input and that sounds like an interesting set up but would not suit my boat and type of sailing.

 

Rest assured, you can certainly use as little as 3.5hp for a two ton yacht & 5hp is ample.

 

I used a two-stroke, long shaft Tohatsu 3.5 to power a 7.7m loa, long keeled Folkboat weighing 2000kg for five years - no issue docking in the marina. However you MUST buy the lowest pitch prop so the engine will reach max rev's (around 5000 rpm from memory). This is critical - its the prop that drives the boat & the standard prop won't let the engine develop its rated revs. I went to the extent of measuring the revs under load & testing three different props to find the right one.

 

This set up WILL push a two ton Folkboat in strong winds & flat water such as inside a marina no problem. I picked up my Westhaven swing mooring dozens of times in 20 to 30 knots over five years. However I didn't use the engine until I was inside Westhaven, for example I wouldn't even have tried to motor from North Head to Westhaven against a 20 to 30 knot SW - that's what sails are for.

 

My reason for using such a small engine was weight - that Tohatsu weighs 12.5kg, so it was easy lift off the transom & into the boat. My previous engine was a Yamaha 5hp two stroke, plenty of power but at 21.5 kg it was too awkward to lift off & put in cabin.

 

When pushing yachts - propeller choice can be more important horsepower.

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Of course small outboards will move a boat around a marina and on fine sunny calm days. The weight of outboards, and cavitation are the downside. A 15hp on a stern bracket is a monster, if its a 4 strokes it's worse. Plus on the 4stroke is the reduced noise. We replaced a 10hp diesel with the 15hp Honda. Half the weight and more grunt. The fuel is in vented lockers with all lines run in conduit. I did have an 8hp 2stroke on my SR. 80% of the time it was fine although coming up the ditch in a westerly on an outgoing tide was too much.

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After being with her all evening, the man couldn't take another minute with his blind date. Earlier, he had secretly arranged to have a friend call him to the phone so he would have an excuse to leave. When he returned to the table, he lowered his eyes, put on a grim expression and said, "I have some bad news. My grandfather just died." "Thank heavens," his date replied. "If yours hadn't, mine would have had to!"

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After being with her all evening, the man couldn't take another minute with his blind date. Earlier, he had secretly arranged to have a friend call him to the phone so he would have an excuse to leave. When he returned to the table, he lowered his eyes, put on a grim expression and said, "I have some bad news. My grandfather just died." "Thank heavens," his date replied. "If yours hadn't, mine would have had to!"

 

WTF?

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Hey guys thanks for some food for thought so far. Excellent stuff.

Interesting stuff about the pitch and propellor. To the folkboat guy (johnmac), I thought their displacement was nearer 2 &1/2 ton?

 

As far as two stroke outboards go--I know you can still buy them, but I thought they were on the way out for various reasons?

 

Update on the electric idea--overseas retailers will not sell direct to overseas clients ( I know 'cause I phoned and asked) and cut into the local retailers, and even if they did the cost to have the special shipping required for anything containing lithium batteries is cost prohibitive.

That's the end of the electric idea.

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I have a 25 footer, I have two outboards, A 7.5 hp and a 4 hp. I use the 4 hp when in the harbor and it is fine and will push me into a 20 knot head wind with hardly any loss of speed if the waves are still small. I have put a lower pitch prop on it so it can use its power. The lower weight of the smaller motor is great with lifting it on and raising it etc.

The 7.5 I take when cruising, I was so impressed with the lower pitch prop on the small motor that I tried to find one for the 7.5, but cannot find one. Not all manufacturers make low pitch props.

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I have a 25 footer, I have two outboards, A 7.5 hp and a 4 hp. I use the 4 hp when in the harbor and it is fine and will push me into a 20 knot head wind with hardly any loss of speed if the waves are still small. I have put a lower pitch prop on it so it can use its power. The lower weight of the smaller motor is great with lifting it on and raising it etc.

The 7.5 I take when cruising, I was so impressed with the lower pitch prop on the small motor that I tried to find one for the 7.5, but cannot find one. Not all manufacturers make low pitch props.

 

What make is the 4hp, and is it 2 or 4 stroke?

Cheers.

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