need new motor
- Thread starter walkingwarship
- Start date
It can also depend on your needs:
If you only motor off a dock or ramp in a lake with no high winds or current and not far to go, 4hp might be fine. I used a 4hp Mariner on my C22 in such a circumstance, and I was never sorry.
On the other hand, if you motor into headwinds or current, or you have a distance to go, more horsepower will be needed.
You also need to check on the motor bracket on your boat. It is rated for a certain horsepower and weight.
What motor came off the boat? That might be a good guide too.
Thanks,
Andrew
If you only motor off a dock or ramp in a lake with no high winds or current and not far to go, 4hp might be fine. I used a 4hp Mariner on my C22 in such a circumstance, and I was never sorry.
On the other hand, if you motor into headwinds or current, or you have a distance to go, more horsepower will be needed.
You also need to check on the motor bracket on your boat. It is rated for a certain horsepower and weight.
What motor came off the boat? That might be a good guide too.
Thanks,
Andrew
I had a 6hp 2 smoker on mine. It moved it well. The areas I sail are tidal and fast flowing in certain areas. The 6 was enough to overcome the forces.
I have a 4hp 4 stroke on my 23. It's an inland lake, no current, works fine. The guy in an adjacent slip uses a trolling motor on his S2 6.9.
That's the real difference; if you're in a location where a motor is a necessity to get to safe cover in deteriorating conditions, then think about your worst case scenario. With some manufacturers, there is little difference in power head between 4-6 hp and so they usually weigh about the same. Stepping up to an 8hp will be a larger power head and (I think) two cylinders.
And then there's the length. An extra long shaft is really optimal. I have a 20" shaft and it pops out in waves unless I'm moving well enough to drive the stern down. My prior motor was a 25 inch shaft and it did better. Your choices to find a 25" shaft are limited. A Tohatsu 6hp and a Honda 8hp come in that length. I do not think Suzuki or Merc offer it.
That's the real difference; if you're in a location where a motor is a necessity to get to safe cover in deteriorating conditions, then think about your worst case scenario. With some manufacturers, there is little difference in power head between 4-6 hp and so they usually weigh about the same. Stepping up to an 8hp will be a larger power head and (I think) two cylinders.
And then there's the length. An extra long shaft is really optimal. I have a 20" shaft and it pops out in waves unless I'm moving well enough to drive the stern down. My prior motor was a 25 inch shaft and it did better. Your choices to find a 25" shaft are limited. A Tohatsu 6hp and a Honda 8hp come in that length. I do not think Suzuki or Merc offer it.
For what it is worth: for no currents this does well enough in gentle head winds. I hope the data is at least useful: from a post made in 2013
I upgraded to a Minn Kota Traxxis 70 from a Motorguide v55 (the v55 controller died after 1.5 years...bummer). The v55 was a little too timid in >20mph winds from a dead start.
The traxxis70 has been good so far. Here I compare the Kipawa 853 prop and the stock prop for the Traxxis 70. Results are interesting? Feel free to stab the data or make suggestions.
I present my data in three ways. Conclusion is always the same. Posted as three individual images. Comments welcome.
http://someyawhoo.smugmug.com/Other/...9683493_6VdVb2
Someyawhoo
I upgraded to a Minn Kota Traxxis 70 from a Motorguide v55 (the v55 controller died after 1.5 years...bummer). The v55 was a little too timid in >20mph winds from a dead start.
The traxxis70 has been good so far. Here I compare the Kipawa 853 prop and the stock prop for the Traxxis 70. Results are interesting? Feel free to stab the data or make suggestions.
I present my data in three ways. Conclusion is always the same. Posted as three individual images. Comments welcome.
http://someyawhoo.smugmug.com/Other/...9683493_6VdVb2
Someyawhoo
Just remember, more power is good for bucking headwinds - you can overcome drag from windage because air is so much less dense than water.
Bucking currents at or over your hull speed can't (easily) be overcome with more power. This becomes less of a concern for longer displacement hulls, because they have a higher max hull speed. For a small boat with a 5 knot hull speed, it doesn't matter if you move the boat through still water at +5 knots, or move the water (current) past the stationary hull at +5 knots, more power will (mostly) just increase the bow and stern waves and very marginally increase speed.
Speed of a wave through the water is determined by wavelength. For a standard displacement hull, the wavelength can only ever max out based on waterline length, so the wave the boat creates can only go so fast. Really skinny hulls can go faster (for example, a Hobie 16 goes a heckuva lot faster than it's "theoretical" max hull speed, but it's not a typical displacement hull shape) and of course planing hulls are not bound by the physics of displacement hulls.
Bucking currents at or over your hull speed can't (easily) be overcome with more power. This becomes less of a concern for longer displacement hulls, because they have a higher max hull speed. For a small boat with a 5 knot hull speed, it doesn't matter if you move the boat through still water at +5 knots, or move the water (current) past the stationary hull at +5 knots, more power will (mostly) just increase the bow and stern waves and very marginally increase speed.
Speed of a wave through the water is determined by wavelength. For a standard displacement hull, the wavelength can only ever max out based on waterline length, so the wave the boat creates can only go so fast. Really skinny hulls can go faster (for example, a Hobie 16 goes a heckuva lot faster than it's "theoretical" max hull speed, but it's not a typical displacement hull shape) and of course planing hulls are not bound by the physics of displacement hulls.
So if I installed a 90hp hyabusa motorcycle engine on a long shaft it wouldn't make a wholr lot of difference because the hull is a displacement hull and not a planing hull?
Warship, if you had a semi-displacement hull like a West Wight Potter 19, you might be able to get it close to planing with a Hyabusa engine.
With a displacement hull, you can get a little bit more speed from more power. But you also will be converting that power to higher amplitude (taller) waves at the bow and stern. My Grandfather's old Chapman's had an image (if I recall) showing that with too much power to a displacement hull, the midships of the boat would start to become unsupported by the water as the bow and stern waves become taller, and this could lead to hull damage. As I recall, the diagram was of a cargo type ship.
With a displacement hull, you can get a little bit more speed from more power. But you also will be converting that power to higher amplitude (taller) waves at the bow and stern. My Grandfather's old Chapman's had an image (if I recall) showing that with too much power to a displacement hull, the midships of the boat would start to become unsupported by the water as the bow and stern waves become taller, and this could lead to hull damage. As I recall, the diagram was of a cargo type ship.
I originally had a Johnson 9.9 followed by a Merc 7.5 on my O'Day 222. Both were old and unreliable so I finally got a new 6 hp Tohatsu 4 stroke and was very happy with it. It easily moved the boat at hull speed. Even with some bigger Lake Michigan waves, it did fairly well. And was not so heavy (54 lbs if I recall) to be a problem for the motor mount. I had changed that to a Garelik a few years earlier. I always tried to use pure gas to avoid problems with ethanol.
I've got a few pictures of the modifications on my album http://forums.oday.sailboatowners.com/album.php?albumid=2157
Dave
s/v Lagniappe
O'Day 25
I've got a few pictures of the modifications on my album http://forums.oday.sailboatowners.com/album.php?albumid=2157
Dave
s/v Lagniappe
O'Day 25
If you get enough wind, many trailerables will plane. It takes a lot of power though to get them up. Most people will give in before they plane as it is scarey as you know what! A big enough motor will plane a small sailboat as well but not very efficiently due to shape of hull. Chief