Aux outboard kicker on a 50' displacement vessel

[ofer]

my question is about HP required to move the boat at 4-5 kts

I have seen threads that discussed this before pros cons etc. i am aware of all that.

I am debating whether the 60HP high trust versions will be enough or i need to go to a 90 or even 115HP

any choice will end up swinging the same prop diameter at the lowest possible pitch.

Suzuki seems the best choice and have the lowest gear ratio highest diameter and lowest pitch.

using Suzuki as an example..

a 60HP HT swinging 14x9 prop and a 90HP swinging same prop.

will the 90HP move the vessel any faster than the 60?

 

[psneeld]

flat water, 4-5 knots even with a strong foul current or headwind and will you be able to keep thr prop deep enough in the water all the time?

 

[Gdavid]

I doubt you will see much difference between 60 and 90 HP, focusing on gear ratio and the diameter of prop that it will accommodate are important as well as the length of the leg. How deep is the center of your transom below the waterline? If you cannot get a outboard this long it will cavitate once you pick up any speed.

I've seen pile driving barges setup with a pair of similar sized outboards mounted on vertical tracks which could be raised and lowered via block and tackle. They extended the fuel lines, hydraulic steering lines and wiring harnesses to provide adequate range of motion and it worked quite well. The bottoms of the barge sloped up at 45 degrees at either ends so the props were receiving a clean water flow.

 

[Mako]

Get home power with an outboard is easily achieved with your dinghy lashed "on the hip". So what can you obtain right now? Say your little 20-40hp outboard pushes you at 3 knots. That's great. But how far are you going to get across the ocean with just a 5 gallon gasoline fuel tank.

Perhaps switch across to a small diesel outboard for the dinghy. An inflatable would be better than a hard fiberglass one.

 

[psneeld]

Ever try hip towing in anything over 2 feet in a smaller boat? Over 4 feet in larger?

 

[ofer]

How deep is the center of your transom below the waterline? If you cannot get a outboard this long it will cavitate once you pick up any speed.

boat has a 6' draft. although the center of the transom is only about 18" below the swim step where the outboard will be mounted on.

 

[ofer]

Perhaps switch across to a small diesel outboard for the dinghy. An inflatable would be better than a hard fiberglass one.

I already have the 27HP yanmar diesel kicker mounted on my 30 foot planning boat. the prop is too small to support moving a larger vessel.

other diesel options are way too expensive and are not considered at this time.

I am planning to keep 100 gal of gasoline on board. i know that will not help me cross oceans but may help to get out of situation.

 

[Lepke]

Ever try hip towing in anything over 2 feet in a smaller boat? Over 4 feet in larger?

Many times.


Tugs do it every day.

 

[ofer]

Ever try hip towing in anything over 2 feet in a smaller boat? Over 4 feet in larger?

i have to admit. i don't understand what this means

 

[Benthic2]

why would you hip tow* instread of a more traditional tow ?

* "hip tow" is when the towboat is tied side by side with the disabled boat.

 

[Gdavid]

Ever try hip towing in anything over 2 feet in a smaller boat? Over 4 feet in larger?

No, sounds miserable, dangerous, destructive for most recreational craft. That said, I imagine you would wait it out for more benign conditions under anchor or sea anchor. Of course an assistance tower is on the clock and isn't going to wait hours or days for better conditions, but for a recreational craft in non- emergency conditions, it would be pretty frustrating to have multiple sources of energy/power and no means to translate it into propulsion. Storing energy in gasoline still seems like a limiting factor. I think an electric or hydraulic coupling of the generator to a propeller would be a more robust approach but that is off topic.

 

[psneeld]

i have to admit. i don't understand what this means

It was in reference to tying to hip tow your big boat with a dingy in more typical conditions than protected waters and/or a short distance to a dock.

Sure...the bigger and more rugged the vessels...the worse conditions hip towing is possible...but at some point.... stern towing becomes the preferred.

 

[ofer]

It was in reference to tying to hip tow your big boat with a dingy in more typical conditions than protected waters and/or a short distance to a dock.

Sure...the bigger and more rugged the vessels...the worse conditions hip towing is possible...but at some point.... stern towing becomes the preferred.

ok although not sure how that relates to my original question.

i am trying to install an outboard centerly located on my swim step. i am debating what's the best OB HP to perform the task without over doing it.

I am aware of all fuel options including electric. Gasoline is the only viable option at this time.

 

[sean9c]

Not an answer to your question but why are you doing this?

 

[ofer]

Not an answer to your question but why are you doing this?

i have a single engine 50' trawler.

i have been boating with my 30 footer for the last 35 years with this setup. I traveled to Cabo in the south and to Juno north in my 30 foot boat.

In all my years i never needed assistance from any agency not the CG back in the day and not vessel assist even though i am a member.

I went over a whale twice in Baja and over a log in Alaska that destroyed my running gear. Its important for me to have extra propulsion that is completely independent of all other systems.

what will it be used for:

help docking like a rear Thruster.

backup steering in case of main rudder malfunction.it will also have its own autopilot.

backup to main power plant and prop.

 

[sean9c]

Huh. That'd take a lot to make it work right. It'll be interesting to see your progress.

i have a single engine 50' trawler.

i have been boating with my 30 footer for the last 35 years with this setup. I traveled to Cabo in the south and to Juno north in my 30 foot boat.

In all my years i never needed assistance from any agency not the CG back in the day and not vessel assist even though i am a member.

I went over a whale twice in Baja and over a log in Alaska that destroyed my running gear. Its important for me to have extra propulsion that is completely independent of all other systems.

what will it be used for:

help docking like a rear Thruster.

backup steering in case of main rudder malfunction.it will also have its own autopilot.

backup to main power plant and prop.

 

[sunchaser]

I think the OP’s question is reasonable. Given the plethora of outboard vessels in the 50’ range out there, doing this is not like a moon shot. The key is assuring structural integrity and security of cable and fuel runs to the vessel.

I recently saw a 30’ Bayliner where the owner had removed main engine and installed a 90 hp outboard. To the OP, if your interested in a picture of this PM me.

 

[Mako]

I recently saw a 30’ Bayliner where the owner had removed main engine and installed a 90 hp outboard. To the OP, if your interested in a picture of this PM me.

That's a very good idea. There are a ton of Sundancers available in the market and the biggest issue is always the engine/IO. Wouldn't be too unreasonable to rip out the old technology, close the hole in the transom, modify the swim platform and install a nice OB on a bracket. Although all in all it's probably cheaper just to buy a nice rebuilt motor/IO and install it fresh.

Post of photo here.

 

[ofer]

I think the OP’s question is reasonable. Given the plethora of outboard vessels in the 50’ range out there, doing this is not like a moon shot. The key is assuring structural integrity and security of cable and fuel runs to the vessel.

I recently saw a 30’ Bayliner where the owner had removed main engine and installed a 90 hp outboard. To the OP, if your interested in a picture of this PM me.

thank you,

I am just looking to move my vessel at 4-5 kts. i would love to conclude that a 60HP high trust would do the job. The 60 HT has the gear case of a 90 or 100 HP with all manufactures. bigger diameter prop is main reason.

if I go to a 90 or 100 HP i am still swinging same diameter prop. I am not sure if the additional 30HP will help for moving a large displacement vessel.

the main component in this setup is propeller size the largest diameter and smallest pitch is best. the question is, will the 60 HP spin the prop at max rpm or not. i realize that prop efficiency is way low and that's all i have.

 

[KnotYet]

The Yanmar diesel outboards in the 36-40 HP range can be bought used and
reconditioned and probably represent the most power you will be able to utilize in
your transom-hung application. It may only take 36HP to move your boat that speed.

Unlike the other options you note, these engines were designed to move heavy,
displacement vessels and feature lower rpm gear reductions.

The bigger prop on a larger, faster turning gas outboard will most likely cavitate
before you can use its greater power output.
Being able to run off your boat's main fuel source is icing on the cake.

 

[RCook]

Yamaha High Thrust models have different gear ratios, as well as larger-diameter and flatter-pitched props. Designed precisely for moving heavier vessels at lower speeds. They also have more thrust in reverse than the conventional models.

My 26-footer's Yamaha 9.9 HT kicker would move the 11,000 lb boat at 4-5 knots. I'd guess the 60HT would work well for the OP's application if it could be mounted appropriately.

 

[sunchaser]

ofer
Just guessing on my part, you'll want to be able to pull about 30 HP to move in smooth water at 5 knots and likely 50 in modest head seas. Running an outboard at mid-range, 2500 - 3000 RPM will generate XX HP dependent upon motor chosen. If the curves and prop set for the 60 HP outboard show the needed horsepower developed at mid-range is acceptable, good. If not, you'll need a larger motor.

The motor chosen should also have suitable thrust to turn the boat in less than perfect weather. Assuming your main rudder is operable you could still use your AP to steer you too.

 

[Mako]

I had purchased previous a Mercury Bigfoot model which had a nice high gear ratio and lots of thrust for my slower, heavy boat. I don't think they make that model anymore but they likely have another high-thrust, similar to the Yamaha.

 

[Xlantic]

I already have the 27HP yanmar diesel kicker mounted on my 30 foot planning boat. the prop is too small to support moving a larger vessel.

other diesel options are way too expensive and are not considered at this time.

I am planning to keep 100 gal of gasoline on board. i know that will not help me cross oceans but may help to get out of situation.

You could change the prop on the diesel outboard that you already have. Find the biggest-diameter, smallest pitch 4 blade prop that fits and that could do the trick.

 

[ofer]

The Yanmar diesel outboards in the 36-40 HP range can be bought used and
reconditioned and probably represent the most power you will be able to utilize in
your transom-hung application. It may only take 36HP to move your boat that speed.

Unlike the other options you note, these engines were designed to move heavy,
displacement vessels and feature lower rpm gear reductions.

The bigger prop on a larger, faster turning gas outboard will most likely cavitate
before you can use its greater power output.
Being able to run off your boat's main fuel source is icing on the cake.

I have the yanmar 27HP installed on my 30 footer for the last 23 years. it's a great motor although the prop is relatively small. I had a 9.9 HT yamaha before that and it had a bigger flatter prop that moved the boat about the same.
there is only one type and one diameter prop available for the yanmar. knowing what i know about the 27 I don't have any confidants that the 36 will do what i need.

 

[ofer]

Yamaha High Thrust models have different gear ratios, as well as larger-diameter and flatter-pitched props. Designed precisely for moving heavier vessels at lower speeds. They also have more thrust in reverse than the conventional models.

My 26-footer's Yamaha 9.9 HT kicker would move the 11,000 lb boat at 4-5 knots. I'd guess the 60HT would work well for the OP's application if it could be mounted appropriately.

yamaha 60hp HT does not have a 25" shaft

 

[ofer]

You could change the prop on the diesel outboard that you already have. Find the biggest-diameter, smallest pitch 4 blade prop that fits and that could do the trick.

I wish i could there is only one diameter one type of prop made for the yanmars

 

[ofer]

thus far Honda has the best solution for 60HP.

high trust version has a 25" shaft and is able to run a 14X9 prop.

finding one is a different story. even new all MFGs are backlogged.

 

[DNT99611]

I have seen kits that add 5 inches to most outboards. I would think 50 hp would be more than enough to do what you want.

 

[sean9c]

Somehow I'm guessing that a 50-60hp outboard is not going to be sufficient to push a, likely, 40+Ton trawler, when it's rough and blowing hard. But, like I said, I'm guessing