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Discussion Starter #1
I am looking at a boat with a fairly new Outboard engine (about a 100 hours) 9.9 four stroke.

Assuming there are no technical issues with it. Are these engines able to run continuously for 70nm, as a motorcycle or a car would, or are this motors limited to short runs?

Any information is welcomed
 

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Marine motors are typically tracked by the number of hours they run, rather than miles covered, as speed will not be consistent.

A properly maintained outboard should be able to run all day, if you like, just not at wide open throttle.
 
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I run my 4 Stroke Honda 2.3 all day at %70, 8-10 hours a day at times. No problem. I carry spare plugs. The motor let's me know when to swap in a clean one.
 

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Ditto for me. My 8 hp 4 stroke at 1/3 throttle will push the boat at hull speed all day no problem. Just keep an eye on the pee (coolant) stream and you should be fine.
 

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Discussion Starter #5
Fantastic. Thank you very much for the information. This gives us a much wider search area to look for a boat.

I have to rely on the engine to bring us home in case we are not confident enough to do the first trip to our moorage fully on sail.

I'll make sure is well serviced before the first trip.
 

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I once had a sailboat fitted with the older model Yamaha 9.9 (which was nearly new at the time) and found it's pee hole would salt up after a fair few hours of continual running on occasion, usually in rougher water. Other than that, it happily ran all day long.
 

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I am not sure recommend a 70 mile delivery for a shakedown cruise, especially if you don't know how to sail. If you can't split the delivery into two days or bring along a skilled sailor, you might want to consider hiring a Captain or renting a trailer.
 

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If you anticipate running the engine for an extended time period on your first run home, take plenty of fuel and a known quantity so you can measure consumption and get to know your new to you engine.
-CH
 

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Discussion Starter #9
We are thinking to split the trip in two days if we decide to buy at that distance. We know how to sail, but we are not experts and will be unfamiliar with the boat. I just want to have a realistic back up plan in case we decide to go on the engine. I am sure we would not resit opening the sails )
 

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If you anticipate running the engine for an extended time period on your first run home, take plenty of fuel and a known quantity so you can measure consumption and get to know your new to you engine.
-CH
Same with oil. Make sure you carry some to top off.

On a new-to-you engine, you probably should take the time to learn its habits...

Run 1 hour, check too see if oil consumption is noticeable. (Probably not.)

Run 5 hours, check oil.

Run 10 hours, check.

As others have said, if you're running 50% power (well, 25%-75%) it ought to go non stop virtually forever. (Yes, you probably should stop every 100 hours to change the oil, or whatever your mfr recommends.)

If you idle too much, you may gunk up the plugs but new 4 strokes seem to have fewer problems with that than old 2 stroke engines did. On the other hand small 4 strokes sip so little fuel (carb jets are so small) that they are sensitive to old or contaminated fuel, and varnish deposits.
 

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We are thinking to split the trip in two days if we decide to buy at that distance. We know how to sail, but we are not experts and will be unfamiliar with the boat. I just want to have a realistic back up plan in case we decide to go on the engine. I am sure we would not resit opening the sails )
Sounds like a reasonable plan. Keep in mind as people suggest running it the motor at 50-75%. My guess is a boat running a 9HP outboard would be doing 5 knots or less unless the conditions are very favorable. Even 30-40 miles a day can be a long stretch at that pace, plan for daylight and weather.
 

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The biggest issue I had when I had a boat with an outboard was motoring when there was some weather. Prop would be out of the water as much as it was in as the boat pitched.
 

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Had a small cape dory with an outboard in a well. In any kind of sea water would rise in the well above air intake and engine would stop. Couldn’t restart it until dried out.
Would suggest OP look carefully if bailout points are available to him and how far away they are. This is more important than the total length of the trip. Would suggest he examine if the bailout points would require anchoring, picking up moorings or entering slips. Ideally if his engine quits he can sail into a harbor and anchor until he sorts himself out.
Would suggest he attend to his anchoring equipment as well as the engine and have a good VHF in case he gets in to difficulties. He needs to be prepared for the possibility of no engine and no wind requiring a tow or assistance.
 

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Given the issues with OBs on sailboats that have already been mentioned, the OP would be well advised to have towing insurance (like TowBoat Us, SeaTow, or part of boat policy).

While the newer 4 strokes are more fuel efficient, until the parameters of the new (to the purchaser) OB are understood, it would be prudent to figure on 1 gal of gas per hour for a 9.9 at full throttle and then allow at least a 100% margin for safety. So, assuming 5 mph speed in flat water (no wind or tide) and 75% throttle, the whole trip would take 18 hrs (straight shot—no detours) and consume 13.5 gal of gas. With a 100%margin, the OP should have at least five 6 gal containers of gas available (along with OB oil if a 2 stroke). If the weather turns nasty or there is a foul tide, the amount of fuel would be greater.

In any case, the OP would be well served to have bail out options planned ahead of the trip.
 

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Discussion Starter #16
Wow, thank you so much for all the excellent advice guys.

We would never be more than 6 miles from land at the widest crossing and we will tow a dinghy behind us. We also plan to enroll with the towing service if the trip happens.

We have all the electronics as well, but no precaution is ever enough on unfamiliar waters with a new boat.

Thank you also for the fuel calculations, the rate of gas consumption is new to me.
 

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It's very difficult to pour gasoline from a 5 gal jug into an outboard motor or into a 3 gal. gas tank. When the boat is dead in the water, it rolls sharply with the waves, and you spill a lot of fuel over the cockpit floor and sometimes yourself. My remedy was to buy 3 portable fuel tanks, and fit each of them with a quick connector. When one runs out, I just disconnect the hose and re-connect it to a full tank and we're under way again in a minute.
 

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Our prior boat was a Niagara 26 with a 10 hp four stroke OB. 25" leg. Mounted on a factory transom cut out, and the prop never over-reved due to pitching in a decade. Trick is to have a boat actually designed from the git-go for an OB. Most boats are not -- you can tell by the bracket mounted on their transom.

We once transited the WA coast and were under way for 46 hours continuous. We used several fuel tanks, and just plugged in a full one when the motor died.... there was no wind to help us on that particular weekend. Burn rate was a half gallon per hour @ 6 kts.

We used a hand cranked fuel transfer pump, but nowadays everyone uses a "rattle syphon". No spillage that way.

Our first engine was a Honda 10, and then we moved up to a Yamaha Hi-thrust 10 (3 to 1 gear ratio).

Happy motoring, and sailing!
 
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I ran my used Honda 9.9Four from Put-on-Bay to Leamington, CA at full throttle in a 7.6 Colombia without fail, it was about a 25 mi. trip. I'm pretty sure I would need to stop for gas to go 70 mi. It was 100 degrees out and no wind and I felt very confident that little motor could have gone to Buffalo if I asked it. Keep oil in it and you should be fine.
 

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Just providing my fuel consumption data for perspective:

C&C 24 with 4hp 4-stroke Tohatsu. I maintain 4kn at 30% throttle. Fuel consumption rate is almost immeasurably small.....say 4-5hrs/gallon (conservative) in fairly calm conditions, waves less than 3ft.

I have a 6 gallon tank and wouldn't hesitate to go the 70NM in a pinch.

Definitely watch the oil levels though; they are harder on oil than I would have imagined for such small engines.
 
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