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Horse Power required to plane like a MacGregor
Just bought an RL24 (sail number 25) and am considering a MacGregor style make over. Does anyone know how many HP are needed to plane the hull? Aiming for about 15 knots top speed.
Paul Van Dyk 27-Aug-2016    Edit    Delete 
Re: Horse Power required to plane like a MacGregor
They are 2 different boats. The big caution is the transom. I think the biggest I have seen is 9.9 and the owner said they where hesitant to push it to its limits. Weight is another factor. My 4 hp makes the back sink just enough to get water spilling in the back - bigger would change her cruising dynamics.
Quinton Smith 28-Aug-2016    Edit    Delete 
Re: Horse Power required to plane like a MacGregor
An RL24 will never plane like a Macgregor.

The Macgregor was designed with powerboat form and sailing as a compromise. the hull is strong enough to take the impacts like falling off a wave at 15 knots and slamming into the next wave. Its stern is wide and has the buoyancy to support larger outboards.

The RL24 is a great sailboat but would be a terrible powerboat. For starters if you could get to 15 knots, the water gushing in the keel case would quickly swamp the boat. The stern is not strong enough for the 40 hp outboard needed to get on the plane and things like the dynamic stability would be unknown, you might never be able to steer the boat due to imbalances between the massive thrust needed to push the boat and the shifts in drag as the boat moves faster than ever considered in its design.

If you want a Mac, buy a Mac, if you want an RL24, you have one.
greg 29-Aug-2016    Edit    Delete 
Re: Horse Power required to plane like a MacGregor
Quinton / Greg,
Thanks for the feedback and I'm still studying the concept.
Have to agree that 15 knots maybe a bit ambitious but 10 - 12 has to be possible.
My RL has a drop keel, with electric winch, so don't think swamping the boat is an issue at 12 knots. Perhaps with a swing keel but even then 12 knots is not that fast.
The current 6 HP is externally mounted on the left hand side. To replace this with a light but more powerful motor, suggest a 15 - 30 HP 2 stroke. These come in at 55kg. I'll do some weight trials with the existing motor to the see what the additional 20 - 30 kg would do.
Mounting the new engine in the well, would be ideal but would need work. This boat was modified for racing . . . but I'm not into that aspect of boating.

PS Greg, I did review the MacGregor the choice was easy enough per below.
- Subject / Winner
- Sailing / RL
- Be able to store fishing gear in the boat without devaluing the vessel / RL
- Cockpit suitable for fishing / RL
- Price / RL by a long shot
- Hull speed / Mac

so add a few HP to the RL and I'm miles in front..... for what I plan to do.
Paul Van Dyk 2-Sep-2016    Edit    Delete 
Re: Horse Power required to plane like a MacGregor
So thoughts as I take friends out to sail but as a family we use the boat to explore up river for weekends. The boat is amazing in that we can pull it up on the beach and launch out quite easily. I invested in a good bimini for shade and some extras for entertaining the kids. Its not quite a Magregor but in my openion the swing keel or drop keel far outweighs the water ballast when it comes to simplicity and reliability. The thing you might consider is not the speed but the noise. I know it sounds silly but honestly it the only thing that makes the ride uncomfortable. If i could figure a way to do 6 knots quieter the boat would be great. Just imagine the fish I could sneak up on.

Just to encourage u. I thought the same way about the boat. As a family boat it has been awesome.
Quinton Smith 5-Sep-2016    Edit    Delete 
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Eromszoox    Edit    Delete 
Re: Horse Power required to plane like a MacGregor
Yes noise is a major pain in the 'ears'! I would rather run a 30 HP at low rpm than a 10 HP at full tilt. The decibels really rise with rpm. Since the plan is to mostly sail, fuel consumption is not a consideration. Weight and transom strength is my current focus.
Paul Van Dyk 9-Sep-2016    Edit    Delete 
Re: Horse Power required to plane like a MacGregor
I had given some notion to do the same thing, only figured one would do much better using a small Jetski motor driving a prop. This way the weight would be farther forward and much lower, where it would help stability. One concern I would have would be directional stability. Yes, the RL is designed to plane and fly along along at 12 knots or so, but it is a whole lot different being pulled from the front of the boat, compared to being pushed from the rear. If you look at a power boat, they have strakes running the length of the hull. This helps the boat to keep facing forward. The RL is smooth and rounded, so there is nothing to keep the rear of the boat from slipping sideways, pivoting on the centerboard. If you ever see guys messing around on jetskis, you will find that if you lean into the corner, the rear of the boat will spin out, because the strakes that will normally dig in are out of the water. If you lean against the corner, the strakes dig in, and the boat turns under full control. The RL does not have these strakes or a hard chine, so if you turn slightly either intentionally or by hitting a wave, there is so much force pushing the boat forward, that it will spin out, because there is nothing to stop it. You could add strakes, but then you slow the boat down under sail because you increase wetted surface.
Daveinet 6-Oct-2016    Edit    Delete 

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