Picking the "right" size outboard

[Quickstep192]

Like most Quickstep 24's, mine came with an 8hp (2 stroke) motor and, like most people, I replaced it with an 8hp 4 stroke. The 4 stroke is considerably heavier than its 2 stroke predecessor and as a result, the boat is heavy in the stern and squats under power. Toward correcting that, I'm wondering if a properly propped 6hp would be adequate. Is there a formula to determine how much motor is needed? In addition to the convenience of being able to get home when there's no wind, I also see a motor as a safety device that can get me home when there's too much wind, or when the weather is hitting the fan. Any thoughts?

[fullkeel7]

I doubt that the weight difference between a 6 hp and the 8 will improve matters much. I think if you have any room fwd of the engines leg, you might be able to adjust the tilt so the thrust could help 'lift' the transom and lower the bow. My Typhoon did the same thing under power(sailed great but would 'squat' under power...4 hp 4stroke).

IMHO, I'd keep the 8 hp and try the adjustment. Even if it doesn't work out, the extra hp can sure come in handy in a pinch...hopefully you will be doing more sailing than powering anyway. Nice boat BTW.

[klem]

There is no specific formula for what size engine you need. You did answer the biggest question which is what role the engine is expected to play. Since you want to be able to push into strong winds, you need some real power and you need the ability to put that power to use. If you plan on pushing into windy conditions, you probably will appreciate having all 8 horsepower. I have spent some time on a Quickstep with a 4hp and it was only good when there was no wind, you couldn't push into 25 knots.

Is the boat only squatting under power? If so, it is likely to be in your engine setup, not weight. How is the engine trim? Are you trying to push your boat past hull speed and causing squat?

Something that is always under appreciated is putting the power into the water. You want your prop as low as possible, not too close to the stern(it will clear the surface in large waves), and as large in diameter as possible. Since your boat has an outboard well, the placement is probably as good as you will get with an outboard. As long as you have a good prop, you probably have a pretty ideal system performance wise although maybe not weight wise.

Do you have a friend with a 6hp that you could borrow and try pushing into a headwind with?

[Quickstep192]

Thanks everyone. The trim is a good point. The shaft on the Honda is a bit longer than on its predecessor. Because the rudder gers wider toward the bottom, the motor can't be trimmed without having the rudder hit it.

[jephotog]

I seem to remember a formula like 4Horse per ton of displacement is a good starting point.

You could get up to hull speed with less, but waves and wind will reduce that. People who are racing will go less to have a lighter stern and just have enough to get out to the start. If you sail on the ocean, or in currents you could go with a few extra HP. You might want to look into shifting some weight down below if the extra weight of the 4 stroke is causing the boat to sit off its lines.

[klem]

Originally Posted by Quickstep192

Thanks everyone. The trim is a good point. The shaft on the Honda is a bit longer than on its predecessor. Because the rudder gers wider toward the bottom, the motor can't be trimmed without having the rudder hit it.

The trim of the outboard in the picture would certainly lead to squatting under power. If you really can't trim it down anymore, could you shim the outboard aft an inch and trim it down some?

[dabnis]

Quickstep,

Lots of input here:
http://www.sailnet.com/forums/genera...-sailboat.html

As said before any way to trim the lower unit forward should help. Don't know what your sailing conditions are but from my experiences in and outside San Francisco Bay you never have too much power.

Dabnis

[RXBOT]

If your boat is 4000 pounds as I think it is 8 hp is minimum you should use. However Tohatsu has a new 6hp, Sailpro with highthrust prop, 25 inch leg, 5 amp gen system and weighs 69 pounds. You might check that out. I wish they would make remote shift and throttle for that size as my 9.9 Merc is 100 pounds but has the remote systems in side of seat locker. (tiller steering)

[tommays]

The prop is everything and most standard props SUCK as there made for planing hulls and don't allow the motor to reach the correct RPM



4hp pushed a CAL 29 AT 8000# 4.5 KNOTS to rescue it from a mooring in Whitestone out to Li to be hauled

[dabnis]

Quickstep,

Just thought about this, how about putting a 1'' or so pad or spacer on the rear (out) side of the existing motor mount, assuming there is still some travel left on the transom clamps. This would probably let you to trim the lower unit about 3" forward or as close to the rudder as you can get.

Dabnis