Forward to 50 seconds? And miss all that boat porn? Surely you jest! Great video! - Jim On Sep 23, 2015, at 4:24 PM, Dave Scobie <scoobscobie@gmail.com> wrote:

Jim:

i've motored against 4kts with a Suzuki 4HP. i know this as i know the setting for a set speed (i usually cruise with motor at about 4.5 knots). GPS says i'm going .5 knots i know the current is about 4kts.

i've pushed a Sage 17 against current with a Honda 2. see this video and forward to 50 seconds.

https://youtu.be/yc0ELdF7Zxs

i was running the motor at 4/5th throttle. this will set a Sage 17 at about 4.8 or 5 kts. in the video i'm going 1 to 1.5 knots over ground. i usually set the motor at 2/3rd or so and cruise at 4.5 kts.

motoring into a headwind the experience will be different as besides current you have wind resistance of the hull and standing rig. once on my folks' Cheoy Lee 32 the wind was blowing so hard the boat couldn't overcome the resistance (boat had a 35-40 HP inboard diesel). in situations like this the question becomes - why are you motoring? you should be sailing.

-- :: Dave Scobie :: former M15 owner - www.freewebs.com/m15-named-scred :: M17 #375 SWEET PEA - www.m17-375.webs.com

On Wed, Sep 23, 2015 at 3:16 PM, James Poulakis <picfo@comcast.net> wrote:

...

So can a 2hp Honda push a loaded (say 2500#) M-17 at its 5.5 knot hull speed against a 4 knot current? I’m hoping it will because I’m tired of doing the “clean and jerk” with my 60# 4hp Mercury.

- Jim M-17 “Spirit”

On Sep 22, 2015, at 3:49 PM, Dave Scobie <scoobscobie@gmail.com> wrote:

...

i'm writing this to assure it is part of the discussions about motor size for the M15, M17, M23, Sage 15 and Sage 17.

these are all displacement hulls that have a hull speed (about 5.2kts for M15 and S15, 5.5kts for M17/S17, and 6.5 for the M23).

the Montomery and Sage hull shapes are not planing type. you may get a little past hull speed but not get the boat on a plane with more horsepower (you will make a bigger wake as the boat tries to climb the bow wave).

so, a larger horsepower motor will not allow you to overcome a current greater than hull speed.

yes, with more horsepower you can overcome wind and get a little help overcoming waves ... but not against current as this is constrained by the boat's hull speed (unless you can get the boat on a plane).

-- :: Dave Scobie :: former M15 owner - www.freewebs.com/m15-named-scred :: M17 #375 SWEET PEA - www.m17-375.webs.com

Jerry Montgomery & I were towed by Stan 'Paintboy' in his old M17 (the old one, not the newer one). Stan used a Honda 2HP in the transom cutout. not a breath of wind and calm seas ... speed was about 4kts. M17 = 1800# S17 = 1300# four guys = (at least) 800# -- :: Dave Scobie :: former M15 owner - www.freewebs.com/m15-named-scred :: M17 #375 SWEET PEA - www.m17-375.webs.com On Fri, Sep 25, 2015 at 10:55 AM, John Schinnerer <john@eco-living.net> wrote:

On 09/23/2015 02:16 PM, James Poulakis wrote:

...

So can a 2hp Honda push a loaded (say 2500#) M-17 at its 5.5 knot hull speed against a 4 knot current? I’m hoping it will because I’m tired of doing the “clean and jerk” with my 60# 4hp Mercury.

It doesn't matter what the current is - hull speed is hull speed. Question is, what is minimum HP needed to push a loaded M17 at hull speed? And, is it worth being able to get the absolute last bit of full hull speed?

AFAIK the curve of power to speed is not linear (not a straight line). The curve gets steeper as you go faster. There is a point of diminishing returns, as you get close to hull speed.

In other words, the last little bit of speed before getting to "hull speed" is going to take proportionally more power to attain than getting "pretty close" to hull speed.

For example, for a boat with a theoretical hull speed of 6 kt., if it takes 1 HP to get to 2 kt. and 2 HP to get to 4 kt., that doesn't mean 3 HP will get you to 6 kt. - it will probably take more than one more HP to get the last .1-.3 kt. of speed.

I experience this personally when paddling - when your body is providing the power directly, you feel the edge between most power-efficient cruising speed and full hull speed pretty clearly. I have to work a bunch harder to get 99% of full hull speed in my kayak than to get 80-90% or so of full hull speed.

So IF (just another example, not based on real world tests) a Honda 2.3 will get an M17 to 5.0 kt. without straining too much, it might still take a 3.5 or 4 HP motor to get to 5.5 kt. without straining too much.

Then it comes down to what is that last .5 kt. (or .2 or .3 or whatever it is in practice) worth in terms of motor cost, weight, fuel use, etc..

Here's a blog I found with a skipper's review of the Tohatsu 6hp SailPro:

https://backbeatsailing.wordpress.com/2013/05/28/tohatsu-6-hp-sail-pro-revie...

From some of the commentary about his choice of this motor instead of the next size up, you can see that he's happy to have a smaller lighter gas sipping motor that will get him "close enough" to hull speed of his boat, rather than the weight and cost and fuel use of 3-4 more HP that it would take to get that last little bit of speed on his hull. And it sounds like this guy is a delivery skipper, in the San Juans, and has done a lot of both sailing and motoring. Also it's a 3000 lb. boat and he's happy with the 6hp...which tells me it's way more than I need for my ~1600 lb. boat.

cheers, John S.

PS - here's an article on HP, thrust, prop, effective HP issues. Based on somewhat larger boats and motors, mid-20 to 30 footers and 10-15 hp, but the concepts are relevant at any HP. http://pages.suddenlink.net/arlyn/sailing/outboards.html No date on this unfortunately, however the motor the author wishes at end of article someone would make sounds a whole lot like the Tohatsu 6hp SailPro so the article probably predates that motor at least. cheers, John S. On 09/25/2015 11:40 AM, John Schinnerer wrote:

On 09/23/2015 02:16 PM, James Poulakis wrote:

...

So can a 2hp Honda push a loaded (say 2500#) M-17 at its 5.5 knot hull speed against a 4 knot current? I’m hoping it will because I’m tired of doing the “clean and jerk” with my 60# 4hp Mercury.

This article: http://www.sailingworld.com/gear/lightweight-outboards-kick

...gives a rule of thumb and also says look at what is known to work: "My rule of thumb here is to start with a two-horsepower engine for small centerboard and keelboats less than 1,000 pounds, and add one horsepower for every 1,000 pounds of displacement....Compare your boat’s dimensions against what existing classes have found to work; for example, a Melges 24 at 1,650 pounds is typically rigged with a three-horsepower short-shaft engine, while a J/80 at 2,900 pounds can still squeak by with a long-shaft, three-horsepower engine. A 1,790 pound J/22, on the other hand, typically uses a four-horsepower long-shaft engine..."

One formula I've found is for minimum HP to move a boat at hull speed:

HP = (Displacement)/((150^2)/(Hull speed^2))

So for an M17 at ~1600 lbs displacement that becomes:

HP = 1600/(22500/30.25) = 2.15

This is more or less congruent with the above rule of thumb.

So the Honda 2.3 or the various 2.5's from other makers ought to be adequate to get hull speed. And more than adequate for cruising a bit below full hull speed, at less than full throttle.

A 3.5 HP would give slightly more than 1 HP margin over the minimum - which is a fairly big margin, percentage-wise.

There is also the issue of what prop is used - is it optimized for displacement sailboat needs, or for small light planing hulls (fishing boats, dinghys, etc.)? Apparently this can make a big difference in actual/effective thrust from a given HP motor.

From my recent research on small outboards, multiple major makers, the weight drop comes when you go under 4 hp. Most makers' 4-6 HP units are ~58-62 lbs.

Most makers' 3.5's are ~20 lbs less, at ~38-42 lbs.

Some 2.5's (Tohatsu, Mercury, Yamaha for example) are pretty much same weight as 3.5's.

Other 2.5's (Suzuki for example) are ~30 lbs. (but Suzuki 2.5 has only 15" shaft model, current options anyhow). Then there's the Honda 2.3 at 31 lbs. (long shaft model).

My research summary at this point:

* Honda 2.3 long shaft would be the choice on the minimalist end, 31 lbs.

* One of the 3.5 long shafts at around 40 lbs. would be an option for more margin of power.

* Anything 4-6hp is going to weight ~60+ lbs.

* If you want a reverse gear instead of rotate motor 180 for reverse, you have to go to a 4-6hp size and weight motor.

* The prop matters - presumably the "sailboat specific" models come with the right kind of prop for our needs but I wouldn't assume that's true for any model not specifically marketed to sailboats.

This is all from available mfg. info on current models. There are no doubt exceptions worth looking at in older models. If anyone has more info, please add it to the pile!

cheers, John S.

-- John Schinnerer - M.A., Whole Systems Design -------------------------------------------- - Eco-Living - Whole Systems Design Services People - Place - Learning - Integration john@eco-living.net - 510.982.1334 http://eco-living.net http://sociocracyconsulting.com

The 6hp Tohatsu Sailpro has a prop specifically intended for use as a sailboat auxiliary. That prop can be fitted to any Tohatsu/Mercury in the 4-6 hp range. ----- Original Message ----- From: "Conbert Benneck" <chbenneck@gmail.com> To: "For and about Montgomery Sailboats" <montgomery_boats@mailman.xmission.com> Sent: Friday, September 25, 2015 3:55:03 PM Subject: Re: M_Boats: overcoming current and hull speed, and motor options On 9/25/2015 1:40 PM, John Schinnerer wrote: Hi John, Propeller pitch is another variable. An outboard motor for a sailboat needs a slow turning large diameter propeller to get maximum thrust. The problem is, that not many manufacturers offer you a sailboat propeller option, and as far as I recall, when they do we are talking about engines in the 6 HP and up range. The old British Seagull engines were slow turning and designed for thrust, not speed; but they were 2 cycle engines. Connie

On 09/23/2015 02:16 PM, James Poulakis wrote:

...

So can a 2hp Honda push a loaded (say 2500#) M-17 at its 5.5 knot hull speed against a 4 knot current? I’m hoping it will because I’m tired of doing the “clean and jerk” with my 60# 4hp Mercury.

This article: http://www.sailingworld.com/gear/lightweight-outboards-kick

...gives a rule of thumb and also says look at what is known to work: "My rule of thumb here is to start with a two-horsepower engine for small centerboard and keelboats less than 1,000 pounds, and add one horsepower for every 1,000 pounds of displacement....Compare your boat’s dimensions against what existing classes have found to work; for example, a Melges 24 at 1,650 pounds is typically rigged with a three-horsepower short-shaft engine, while a J/80 at 2,900 pounds can still squeak by with a long-shaft, three-horsepower engine. A 1,790 pound J/22, on the other hand, typically uses a four-horsepower long-shaft engine..."

One formula I've found is for minimum HP to move a boat at hull speed:

HP = (Displacement)/((150^2)/(Hull speed^2))

So for an M17 at ~1600 lbs displacement that becomes:

HP = 1600/(22500/30.25) = 2.15

This is more or less congruent with the above rule of thumb.

So the Honda 2.3 or the various 2.5's from other makers ought to be adequate to get hull speed. And more than adequate for cruising a bit below full hull speed, at less than full throttle.

A 3.5 HP would give slightly more than 1 HP margin over the minimum - which is a fairly big margin, percentage-wise.

There is also the issue of what prop is used - is it optimized for displacement sailboat needs, or for small light planing hulls (fishing boats, dinghys, etc.)? Apparently this can make a big difference in actual/effective thrust from a given HP motor.

From my recent research on small outboards, multiple major makers, the weight drop comes when you go under 4 hp. Most makers' 4-6 HP units are ~58-62 lbs.

Most makers' 3.5's are ~20 lbs less, at ~38-42 lbs.

Some 2.5's (Tohatsu, Mercury, Yamaha for example) are pretty much same weight as 3.5's.

Other 2.5's (Suzuki for example) are ~30 lbs. (but Suzuki 2.5 has only 15" shaft model, current options anyhow). Then there's the Honda 2.3 at 31 lbs. (long shaft model).

My research summary at this point:

* Honda 2.3 long shaft would be the choice on the minimalist end, 31 lbs.

* One of the 3.5 long shafts at around 40 lbs. would be an option for more margin of power.

* Anything 4-6hp is going to weight ~60+ lbs.

* If you want a reverse gear instead of rotate motor 180 for reverse, you have to go to a 4-6hp size and weight motor.

* The prop matters - presumably the "sailboat specific" models come with the right kind of prop for our needs but I wouldn't assume that's true for any model not specifically marketed to sailboats.

This is all from available mfg. info on current models. There are no doubt exceptions worth looking at in older models. If anyone has more info, please add it to the pile!

cheers, John S.

tohatsu had a complete after market line of props for their motors. The lower the number on the prop such as 4:1 as opposed to 9:1 the less forward movement is made by the prop in one revolution and the more power it can exert on the water. So a 4:1 will travel four inches forward with more power than the 9:1 but with less forward speed while a 9:1 will travel nine inches forward with less power/more speed. On Mon, Sep 28, 2015 at 3:46 PM, John Schinnerer <john@eco-living.net> wrote:

Manufacturers may not, but there are lots of aftermarket props out there. I've only begun to research them...if someone else already has, please post info.

cheers, John S.

On 09/25/2015 12:55 PM, Conbert Benneck wrote:

...

On 9/25/2015 1:40 PM, John Schinnerer wrote:

Hi John,

Propeller pitch is another variable.

An outboard motor for a sailboat needs a slow turning large diameter propeller to get maximum thrust.

The problem is, that not many manufacturers offer you a sailboat propeller option, and as far as I recall, when they do we are talking about engines in the 6 HP and up range.

The old British Seagull engines were slow turning and designed for thrust, not speed; but they were 2 cycle engines.

Connie

On 09/23/2015 02:16 PM, James Poulakis wrote:

...

...

So can a 2hp Honda push a loaded (say 2500#) M-17 at its 5.5 knot hull speed against a 4 knot current? I’m hoping it will because I’m tired of doing the “clean and jerk” with my 60# 4hp Mercury.

This article: http://www.sailingworld.com/gear/lightweight-outboards-kick

...gives a rule of thumb and also says look at what is known to work: "My rule of thumb here is to start with a two-horsepower engine for small centerboard and keelboats less than 1,000 pounds, and add one horsepower for every 1,000 pounds of displacement....Compare your boat’s dimensions against what existing classes have found to work; for example, a Melges 24 at 1,650 pounds is typically rigged with a three-horsepower short-shaft engine, while a J/80 at 2,900 pounds can still squeak by with a long-shaft, three-horsepower engine. A 1,790 pound J/22, on the other hand, typically uses a four-horsepower long-shaft engine..."

One formula I've found is for minimum HP to move a boat at hull speed:

HP = (Displacement)/((150^2)/(Hull speed^2))

So for an M17 at ~1600 lbs displacement that becomes:

HP = 1600/(22500/30.25) = 2.15

This is more or less congruent with the above rule of thumb.

So the Honda 2.3 or the various 2.5's from other makers ought to be adequate to get hull speed. And more than adequate for cruising a bit below full hull speed, at less than full throttle.

A 3.5 HP would give slightly more than 1 HP margin over the minimum - which is a fairly big margin, percentage-wise.

There is also the issue of what prop is used - is it optimized for displacement sailboat needs, or for small light planing hulls (fishing boats, dinghys, etc.)? Apparently this can make a big difference in actual/effective thrust from a given HP motor.

From my recent research on small outboards, multiple major makers, the weight drop comes when you go under 4 hp. Most makers' 4-6 HP units are ~58-62 lbs.

Most makers' 3.5's are ~20 lbs less, at ~38-42 lbs.

Some 2.5's (Tohatsu, Mercury, Yamaha for example) are pretty much same weight as 3.5's.

Other 2.5's (Suzuki for example) are ~30 lbs. (but Suzuki 2.5 has only 15" shaft model, current options anyhow). Then there's the Honda 2.3 at 31 lbs. (long shaft model).

My research summary at this point:

* Honda 2.3 long shaft would be the choice on the minimalist end, 31 lbs.

* One of the 3.5 long shafts at around 40 lbs. would be an option for more margin of power.

* Anything 4-6hp is going to weight ~60+ lbs.

* If you want a reverse gear instead of rotate motor 180 for reverse, you have to go to a 4-6hp size and weight motor.

* The prop matters - presumably the "sailboat specific" models come with the right kind of prop for our needs but I wouldn't assume that's true for any model not specifically marketed to sailboats.

This is all from available mfg. info on current models. There are no doubt exceptions worth looking at in older models. If anyone has more info, please add it to the pile!

cheers, John S.

-- John Schinnerer - M.A., Whole Systems Design -------------------------------------------- - Eco-Living - Whole Systems Design Services People - Place - Learning - Integration john@eco-living.net - 510.982.1334 http://eco-living.net http://sociocracyconsulting.com