Full Throttle - Outboard Motor

[Plymouth Sailor]

Opinions appreciated on a simple question. I've just upgraded from an 8 to a 15hp outboard for my 25' sailboat. Since these motors 2-15hp are used as well for dinghys, skiffs etc with less resistance I would imagine they are under less stress with a lighter craft. Would I damage my motor on a 4000 lbs sailboat in full throttle as opposed to a 200 lbs dinghy?

 

[justsomeguy]

Would I damage my motor on a 4000 lbs sailboat in full throttle as opposed to a 200 lbs dinghy?

No, but I'd like to see a 15 horse on a 200 lb. dinghy.
At full throttle, that could damage both!

 

[dlochner]

You won't damage the engine by running it at full throttle, but you will waste a lot of gasoline.

Sailboats are displacement hulls with a theoretical maximum speed of about 1.22 times the square root of the waterline length. (No need to debate the various interpretations of hull speed here.) What that means is once the boat gets to hull speed applying more power does very little to increase speed. All that happens is more fuel is burned pushing water.

A 25 ft boat has a hull speed around 5 to 5.5 knots (about 5.5 to 6 mph) Once the boat reaches that speed adding more throttle does not increase speed, so you will seldom if ever run the outboard at full throttle.

Powerboats that can plane will use extra HP and throttle to go faster, because they plane and are not bound by hull speed.

A larger outboard on a sailboat provides more power to punch through chop and to go up wind, it won't increase boat speed. Make sure the outboard bracket can support the extra weight and torque from the larger motor.

 

[Charlie Jones s/v Tehani]

I have an 8 HP Yamaha in my 25 footer. Running at the "start" setting gives me hull speed.. Running WOT squats the stern and sucks water into the cockpit via scuppers. I've run the boat from South Texas around to Annapolis Maryland, and all through the Bahamas. Silly to run WOT

And I have no iudea wh ere the Italics came from, but they won't go away !!

 

[rgranger]

And I have no iudea wh ere the Italics came from, but they won't go away !!

@Charlie Jones s/v Tehani On a PC, control "i" will toggle italics and control "u" will toggle underline and control "b" will toggle bold. Do all three and you get this.

On a Mac, use the apple key instead of the control key.

 

[dlochner]

On a Mac, use the apple key instead of the control key.

That would be the quadrille key. Also known as the command or CMD key.

For some strange unimaginable reason, Microsoft and Apple agreed on basic keyboard commands, almost.

 

[rgranger]

That would be the quadrille key. Also known as the command or CMD key.

For some strange unimaginable reason, Microsoft and Apple agreed on basic keyboard commands, almost.

@dlochner I started on QuatroPro on an old 386 back when it was still dos (1989). Most of the command key strokes that you used to have to use before windows existed on a PC still work on Excel. My students think I'm a spreadsheet wizard.

 

[Crazy Dave Condon]

Sailboat manufacturers designed sailboat transoms for a max of 10 hp as generally the higher thrust would cause the boats to plow thru the water above 10 hp. due to the hull being a displacement hull and not a plaining hull. Only were the sailboat hybrids for power/sail had the beefed up transoms found on plaining hulls to include the MacGregor 26, Hunter Edge 27 and so forth.

 

[Rick486]

No, but I'd like to see a 15 horse on a 200 lb. dinghy.
At full throttle, that could damage both!

Well, the weight of my a 10.6 plus my 15 Yamaha is around 250 lb. Excluding the motor, the dinghy weighs about 160 lb. Goes fast

 

[justsomeguy]

Goes fast

You crazy kids! Do you go WOT?

 

[rgranger]

In high school... a buddy of mine's father owned a welding shop. He had an 18' aluminum flat bottom fishing boat and we reinforced the transom... then put an old 65hp Evinrude on the back. Two of us had to sit near the front to keep the O.B. out of the water.

... that thing was SICK!

We were riding on the prop most of the time.

 

[Rick486]

You crazy kids! Do you go WOT?

Never, really, with just myself, wife , and 2 dogs. But I have had 4 adults aboard and easily planed across the harbor. As you know, the trick with planing is open the throttle pretty far until she gets up on plane, then ease off a bit. When I bought the rig I debated a 9.9 vice the 15. The salesman said the 9.9 would easily plane with 2 aboard, but would struggle with 4. And the 15 was only like $150 more on a $4500 purchase of motor and boat, and the weight difference was minuscule. So what the heck. Rather have it and not need it, than need it and not have it.

 

[Jackdaw]

Sailboat manufacturers designed sailboat transoms for a max of 10 hp as generally the higher thrust would cause the boats to plow thru the water above 10 hp. due to the hull being a displacement hull and not a plaining hull. Only were the sailboat hybrids for power/sail had the beefed up transoms found on plaining hulls to include the MacGregor 26, Hunter Edge 27 and so forth.

Of course an edge case, but the ClubSwan 50 racer/cruiser not only planes under spinnaker but will plane under diesel power, an AMAZING feat.

 

[rgranger]

Those are great looking boats. I'm not sure I would call it a cruiser but I'd be happy to go cruising on one.

 

[Crazy Dave Condon]

It is the transom boys I am referring to just like my big posterior end

 

[capta]

Our 160# Zodiac goes over 35 knots with the 15 hp outboard on it. Way too light and dangerous to go full throttle with only one aboard on any but the calmest day.

 

[Chief RA]

My 9' inflatable handles my 15hp 2 stroke Evinrude with relative ease. 26 mph with 2 adults aboard. Chief

 

[justsomeguy]

Where you been, @Chief RA ?

 

[Chief RA]

Mostly Bodega Bay hanging out on Compass Rose. Seas and winds bad this year. Had limited online access. Back home in Oroville until end of Dec. and then down your way to Arizona again. 15th year this trip. My best, Chief

 

[justsomeguy]

Mostly Bodega Bay

Just watched Hitchcock's The Birds a few days ago.
Hope all's well!