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Old 11-08-2016, 08:37 AM   #1
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Yamaha 9.9 high thrust aux engine+ms 34t 20,000 lbs

Hi to all!

I was wondering what would your thoughts be on the following subject:

Use of a Yamaha 9.9 High Thrust as an auxiliary engine in case something goes wrong with the main engine. The boat is a Mainship 34 TRAWLER, 2006 model, single Yanmar 370 hp, at 20,000 lbs weight. The aux engine will be mounted on the swimming platform, most probably on the left side of it, so that the propeller can catch the water without any obstruction from the center line tunnel, main propeller etc. The boat is not used on a lake or river, but on the sea, so it is possible to have to deal with some short of wavy seas, occasionally.

So, the question is: Will the Yamaha be able to push this boat with some minimal speed of say 2 to 3 knots, in order to get safely to the closer shore, in case main engine fails?

What do you think?

Thanks much, once more, for your thoughts.

Paris
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Old 11-08-2016, 08:44 AM   #2
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the subject hs been tossed around with 2 main thoughts that usually evolve from what I remember......


generally the little kickers will move the boat but generally not much against wind or current. if there is any pitching action, the motor will lift clear or cavitate so much it will be of little value and you may destroy it.


in calm waters where you just want to get ot of a shipping lane or into a cove that is downwind/down current...it may be worth it.


before getting all excited by it, try using that or similar engine on a dingy and try it...you may see similar enough results to convince you one way or the other remembering the pitching issue wont be there.


the other mindset is...if you think you need backup power, just do it right if you can. Otherwise just make sure you can always anchor quickly and safely when you get underway...and make sure your maintenance is good.
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Old 11-08-2016, 08:58 AM   #3
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Not effective in the ocean, moderate wave action will be cavitating the prop like crazy, seen plenty of fisherman mount a small outboard on swing bracket next to main and most didn't work unless in ideal conditions, plus that's a pretty sizable boat with plenty of windage.
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Old 11-08-2016, 03:59 PM   #4
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Thanks for the input.

P.
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Old 11-09-2016, 06:57 AM   #5
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Quote:
Originally Posted by Paris View Post
Use of a Yamaha 9.9 High Thrust as an auxiliary engine in case something goes wrong with the main engine. The boat is a Mainship 34 TRAWLER, 2006 model, single Yanmar 370 hp, at 20,000 lbs weight.

So, the question is: Will the Yamaha be able to push this boat with some minimal speed of say 2 to 3 knots, in order to get safely to the closer shore, in case main engine fails?

Would it be a possibility to instead carry a dinghy with a 15- or 20-hp outboard? Then if necessary, use the dinghy -- with more hp -- to tow the Mainship, either behind or on the hip?


Just brainstorming alternatives...

-Chris
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Old 11-09-2016, 07:16 AM   #6
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How far will the outboard need to move the boat?

How much fuel will this require?

Assuming it is a gas (not diesel) outboard, how will you store this amount of gas?

How often and how will you replace the fuel to assure it isn't stale when you need it?
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Old 11-09-2016, 08:32 AM   #7
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With the OB out there on the swim platform, you better expect it to get submerged a few times from waves. Mounted on the swim platform permanently will always be in the way, especially when tilted up when not in use. Pushing the boat any real distance will need at least a 6 gal tank full of gas. 5-10 hours at half throttle and whatever speed you get.
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Old 11-09-2016, 11:04 AM   #8
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For a reference point our displacement hull requires an extra gallon of diesel per hour to move when we carry 20,000 pounds of fuel. This pretty much agrees with gerrs calculations. I imagine you are going to need at least a 30hp outboard to have any success.
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Old 11-09-2016, 12:55 PM   #9
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it only takes about 35hp to move my boat at an average of 6.3 knots...


what do you want to do with this outboard? Cruise...or just run down wind, down current to safety? 9.9 or even less may be capable of that...I will be experimenting with my dingy and 8hp 4 stke this winter for grins and giggles.
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Old 11-09-2016, 03:59 PM   #10
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Yamaha 9.9 high thrust aux engine+ms 34t 20,000 lbs

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This Manatee owner made an interesting hard mount for his large-engined dingy. Allegedly he can push the boat with it when needed.

Dinghy and Davits
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Old 11-09-2016, 05:05 PM   #11
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WE had a 56HP Yanmar saildrive as a wing back-up engine on a 65,000lb trawler (280HP main). The Yanmar was capable of 4-5Kt under average conditions. OK for back-up but slow!!I have seen 46ft sailboat (est 20,000lb) pushed by dinghy with 10HP outboard under calm conditions but would not want to bet the boat on such a system. In fact many sailboats only have small HP inboards.
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Old 11-09-2016, 05:12 PM   #12
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Why not fit an electric motor to the prop shaft via pulley set up? seems a simple solution . Then just run the generator and use the battery bank ???
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Old 11-09-2016, 05:47 PM   #13
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Quote:
Originally Posted by gaston View Post
Why not fit an electric motor to the prop shaft via pulley set up? seems a simple solution . Then just run the generator and use the battery bank ???
But not if it is a shaft or prop problem causing power loss. For the same reason, I think an inboard wing auxiliary needs its own shaft. But it all costs $, and the generator solution does cover some of the problems.
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Old 11-09-2016, 07:26 PM   #14
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Bruce,
If you have a generator.
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Old 11-09-2016, 08:21 PM   #15
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Quote:
Originally Posted by ranger42c View Post
Would it be a possibility to instead carry a dinghy with a 15- or 20-hp outboard? Then if necessary, use the dinghy -- with more hp -- to tow the Mainship, either behind or on the hip?
I did this once to hold a 30 foot cruiser off of a lee shore in the Straights of Georgia one snotty afternoon..never again (if I can help it!)

It was very difficult and dangerous to rig the dingy and motor and then setup the tow in steep chop because we had lost propulsion and could not hold the boat into the wind. I was taking a beating and just barely holding headway due to the windage on the cruiser.

The Canadian Coasties showed up 10 minutes later with a twin 50 hp Zodiac, that is what it took to get us in safely.
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Old 11-09-2016, 09:26 PM   #16
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I have a 9.9 Mercury two-cycle that I plan to bracket on my swim platform ladder for emergency maneuvering, but I haven't tried it out yet. I left another option open when I installed my genset in a new hatch under the veranda. The photos below show the genset crankshaft directly over the prop shaft. A PTO setup to the prop shaft could be done from that position. The upward contour of the hull in that area would also permit a separate shaft and folding prop with an electric or even hydraulic motor using the genset power, but you'd still be hard pressed to get much more than a 3 knot capability out of that 10 or so HP. With a bigger genset, maybe.
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Old 11-09-2016, 10:07 PM   #17
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BTW, swim platform outboard brackets are available from several sources on e-bay.

Outboard Motor Bracket For Swim Platform white with lip | eBay
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Old 11-09-2016, 10:10 PM   #18
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Larry way to go .... I like it!

Gone Farrell,
Would a 4-500' anchor rode been able to keep you off the beach?
One of the reasons I have a 435' rode is for situations like you had.
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Old 11-09-2016, 11:38 PM   #19
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Eric,
Hard to say. Things were happening fast, I estimated we were no more than 20 mins from lee shore rocks in typical 3 to 4 foot chop. I don't recall the depth, we were some distance from shore. My experience with really long rodes is minimal, but it always bugged me that it can be hard to tell if I'm dragging in snotty conditions.

I would consider it a back up plan to go deep with an anchor, another reason to have a long stern tie reel on board!
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Old 11-10-2016, 03:25 AM   #20
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Paris- Rather than invent the wheel on the subject, Here is a site on the forum

'Get Home' Outboards

Scroll down to # 33 and read Murray's post. He and later I, have this mount on our respective swim steps.

In my case I use a 9.9 Hi Thrust which is the equivalent to a 15 hp motor. It might be a tad light for your boat, yet it pushes our 28 foot 12,000-13,000# boat at 4.5 knots at 3/4 throttle. Our swim step is 8 inches from the water so our bracket is 6" high for a total of 14" which is the normal height for a transom mount were this a 'skiff' application.
To address the concern of cavatation, one can purchase a 'long shaft' model which I recall is a 25' length (I may be off on this measurement). Anyway, we have been in waters that test the depth factor with no dreadful effect. On an extreme wave one might have a moment but to date we have not had concerns. Note: This was a test of the unit to see just that, how it handled.
Our rudder apparently is large enough as we can steer the boat in a normal method with the boat's steering and do so as we use the OB for salmon trolling where the boat under main engine power is too fast for the gear.
I would add that the benefit of this application Murray and I have employed allows the engine to be out of the way from having the shaft sticking out when raised.
In total of all the mount methods I believe this is the most sanitary, ease of motion, and provides the safest environment for the protection of the OB when not in use.

Regards,
Al 27' (30'overall) Marben Pocket Cruiser
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