repowering; what shaft length

[csm]

We're moving up from 70hp to a 90 etec, and I'm wondering what the common concensus is on shaft length. My current 70 is 20" and pushes forward fine but is almost uncontrollable in reverse. I realize the huge freeboard on the 26X is the main culprit, but I was wonder if perhaps a 25" shaft would improve backing??? Any other pros/cons of 25' vs 20" shaft.
thanks in advance.
Chris

[Crikey]

Chris, I can't quite visualize the 'uncontrollable in reverse' scenario you are mentioning. Sure, no boat is going to be as pointable, under power, as in a forward direction but I've never noticed an adverse mention about this behavior, on this site. Something else must be going on.
The 20" shaft length is the correct one. The only thing you need to ascertain is whether the plate (cavitation plate) is level with the bottom of the stern/hull junction. Going too low with this will add drag and reduce your speed, and fuel efficiency.
Perhaps the PO mounted the engine too high, and this is the source of your trouble?
Got any pictures?

Ross

[DaveB]

Stay with the 20 inch shaft and keep your centerboard down about 10 inches (thats about 2-3 inches less on the centerboard line).
Also have at least 1 rudder down and you should back up in any direction.
No sailboats back up very well, at least we can turn the outboard were inboards cannot.
In strong cross wind have your ballest full.
Dave

We're moving up from 70hp to a 90 etec, and I'm wondering what the common concensus is on shaft length. My current 70 is 20" and pushes forward fine but is almost uncontrollable in reverse. I realize the huge freeboard on the 26X is the main culprit, but I was wonder if perhaps a 25" shaft would improve backing??? Any other pros/cons of 25' vs 20" shaft.
thanks in advance.
Chris

[csm]

Sorry Crikey, uncontrollable probably wasn't the best description; lets say, very hard to control, especially in our typical 15+ winds. I have tried the ballast trick, as well as rudders down (I'm thinking that's where those prop scars came from ) haven't tried the CB, but I'll give it a shot. The motor is professionally installed, so it's probably more of an operator vs equipment issue. I'm usually in a hurry to depart the dock; I probably need to slow down and "tweak" the boat a bit.

[Kittiwake]

....keep your centerboard down about 10 inches ....
Also have at least 1 rudder down .... have your ballast full.
Dave

.... My current 70 is 20" and pushes forward fine but is almost uncontrollable in reverse. ....
Chris

Dave, with regard to backing up, I don't fully agree with your above suggestions:
- I do agree that having the centerboard down a bit should help (although I rarely do in docking situations because I'm liable to forget it in the shallows that I inhabit)
- I do agree that full ballast is a good move in making the boat less twitchy
- but if anything, I find the rudders make backing more crazy: my guess is that they sort of nail the stern to the water in terms of sideslip and also increase directional change abruptness of the stern, while leaving the rest of the hull to swing (eg. into the dock!). This is magnified considerably if you give the reverse gear excessive throttle (which is easy to do with the E-tec 60 stock throttle - you have to tell yourself, "just a smidgen of reverse throttle!"). I suppose if the centerboard is down though, as you suggest, this phenomenon would be reduced.
Kittiwake

[seahouse]

Hey All!

Some of the difference could be that you have an M, Kittiwake, and therefore you have a daggerboard, and not a centreboard like the X. When partially retracted the centreboard presents a shallower, more keel-like configuration that changes the location of the centre of lateral resisitance, or, in slow maneuvering, the point of pivot for the turn.

A daggerboard maintains its effective position along the hull regardless of it degree of extension, and also presents a more “pivot-around-able” vertical profile.

Like typical powerboats the Mac under power is more controllable turning to starboard than port when maneuvering forward, and is more easily controlled turning to port than starboard when backing.

I’ve also found that when I reverse out of a slip it is better to not add too much power all at once, but to ease it up instead. Too much initial power will cause turbulence that, when the centre/daggerboard reaches that point in the water, can push it sideways. Same way the propwash pushes sideways on the vertical rudder of an airplane on takeoff power, inducing yaw.

And even though the prop shaft is normally parallel to the longitudinal axis of the boat and direction of travel, I have noticed that there is still some prop walk induced with a stronger burst of power on our boats. This characteristic is usually more prominent on larger (keel) boats where the shaft is oriented at a downward angle relative to the direction of travel.

I do have a dealer-installed after-market throttle control that is better-suited to the Mac binnacle than the Evinrude factory options, so that might be giving me an advantage in power control.

Once you have way, and are turning, and want to arrest backward motion, then I like to use a good strong, but short “power pulse” on the throttle to swing the stern around, and then add power again when I'm ready to move away forward.

I agree with full ballast, ~25% daggerboard (can be more, but I have yet to use much more), both rudders down, as being a good configuration to optimize maneuvering in confined areas. I would suggest using the same configuration every time, once you establish what that is, so that you will be familiar with exactly how the boat will react to steering and power input with the fewest necessary variables.

I related my very first experience at the helm of a Mac, when I first launched it this spring, elsewhere on this board. Started backing away from the trailer with empty ballast, dagger and rudders up. I backed most of the length of the marina with the centerline of the boat at a 45 degree angle to the direction of travel! I had great control over the track I was taking, but not so good control over the direction the boat was facing! Until I could get the dagger and rudders down.

If the motor is correctly mounted on the transom for both shaft lengths there will be no difference in the handling of the boat, because the part of the motor in the water will be the same in both cases, assuming equal range of steering motion. In both cases the relation between the anti-cavitation plate and the bottom of the hull at the stern should be the same.

The extra shaft length is there to allow for mounting on a higher transom, and not to allow the motor to extend into the water farther for more control.

Regards- Brian.

[DaveB]

Kittiwake,
The post was for a Mac.X with a centerboard and what I have posted is correct. You have a daggerboard on the M and there for a diffrent method would apply tho I would think you still could bring the daggerboard down a bit for control.
The Mac.X with the centerboard down 10 inches acts like a skeg for direction control. The M Daggerboard has much less surface area in the water at 10 inches than the Mac.X for directional control.
Regardless what boat you have one needs to make a bit of headway or stearn way to have the rudders and daggerboard/centerboard to take effect.
Dave

....keep your centerboard down about 10 inches ....
Also have at least 1 rudder down .... have your ballast full.
Dave

.... My current 70 is 20" and pushes forward fine but is almost uncontrollable in reverse. ....
Chris

Dave, with regard to backing up, I don't fully agree with your above suggestions:
- I do agree that having the centerboard down a bit should help (although I rarely do in docking situations because I'm liable to forget it in the shallows that I inhabit)
- I do agree that full ballast is a good move in making the boat less twitchy
- but if anything, I find the rudders make backing more crazy: my guess is that they sort of nail the stern to the water in terms of sideslip and also increase directional change abruptness of the stern, while leaving the rest of the hull to swing (eg. into the dock!). This is magnified considerably if you give the reverse gear excessive throttle (which is easy to do with the E-tec 60 stock throttle - you have to tell yourself, "just a smidgen of reverse throttle!"). I suppose if the centerboard is down though, as you suggest, this phenomenon would be reduced.
Kittiwake

[csm]

Seahorse wrote:

Like typical powerboats the Mac under power is more controllable turning to starboard than port when maneuvering forward, and is more easily controlled turning to port than starboard when backing.

I’ve also found that when I reverse out of a slip it is better to not add too much power all at once, but to ease it up instead. Too much initial power will cause turbulence that, when the centre/daggerboard reaches that point in the water, can push it sideways. Same way the propwash pushes sideways on the vertical rudder of an airplane on takeoff power, inducing yaw.

Thanks to all my fellow Macsailors; is this not the best site ever ??? Pitch out a general question and BOOM every aspect is addressed.

Here's my PERSONAL takeaway;

REPOWER CHECKLIST:
20" shaft 4 sure

LAUNCH CHECKLIST:
1. ballast full.
2. centerboard...15-30 degrees depending on depth.
3. rudders: won't put them down unless I'm in cramped quarters and deep water (I think the prop scars came from partially deployed rudder in shallow water).
4. factor wind/current and plan for port side reverse departure if practical.
5. CHILL OUT (make that #1)

[ronacarme]

Our 2001 X runs a Honda 9.9 which my dealer verifies has a 25 inch (extra long) leg. It has worked perfectly in driving into 4-5 ft waves with prop staying fully immersed with no cavitation or ventilation, unlike the shorter legged Nissan 8 on my old 1988 26D.
A 20 inch leg might have less drag at planing speeds, but that is not an issue on our X because a 9.9 would not drive it beyond hull speed regardless of leg length. For us the critical requirement is reliable, efficient powering of the boat into big waves.
Ron

[Rudder Nonsense]

When concidering shaft length, take into account the body of water you will be riding. If its a flat body a shorter shaft will stay in and you will have less drag at high speed, but if you ride a bumpy lumpy body, a shorter shaft make come out quite often causing you to loose control and could damage your shaft. A longer shaft will stay penetrated and working.

***Disclaimer*** Author disallows any responsability for sexual inuendos as it's not his fault it's off season and peoples minds are elsewhere.

[mastreb]

I do have a dealer-installed after-market throttle control that is better-suited to the Mac binnacle than the Evinrude factory options, so that might be giving me an advantage in power control.

Which throttle do you have? I have to replace the stock ETEC throttle--I don't think there's been a time someone hasn't hit it while clambering around the cockpit.

[mastreb]

Backing out of the public docks in San Diego, turned to port with all boards fully down and ballast in, 3 knots, the boat is still 25 degrees off heading to starboard every time. When backing, the boat points with the currents and the wind irrespective of the Heading no matter what you do in my experience. But it goes where you point the motor (even more reliably than low speed forward, where the currents and wind affect the direction of travel rather than just the attitude of the boat). I back out routinely in restricted lowspeed maneuvering for this reason. Standing backwards at the helm facing aft works well.

Matt

[Tomfoolery]

haven't tried the CB, but I'll give it a shot.

This caught my attention right off. When I first got my last summer, I was well used to a keel boat, with fixed prop. Only steering was via the big barndoor rudder, plus some prop walk that you can use to your advantage if you want. The keel made it pivot like it was on a pin when docking.

With the and it's high freeboard, no ballast, rudders up, and centerboard up, it was like a dog running on ice. I blew sideways into another boat's anchor (gotta repair that this spring), and was all over the place. My FIL (who has a long single-screw trawler background) reminded me that it'll act like a powerboat, and I need to adjust my thinking. Helped, but not hugely, as I don't have any PB experience.

It took a bit of practice, but found pretty quickly that ballast in, rudders full down (usually just one), and centerboard full down (I have the depth for it at my dock) was the way to go. It doesn't turn as well as most keelboats, IMO, but now that I have the knack, it's not bad, and I usually do it the same way so the feel doesn't change. Sometimes I have to pull the CB up a bit at different places, but the feel doesn't change so much that it feels like a different boat, so I'm happy. I also sometimes don't use the downhaul on the rudder if I suspect I'll scrape bottom, but that's just at docking speeds where the rudder really isn't trying to fold back.

My engine turns with the rudders - I don't know why there would be a problem with interference, but I have a BF50, so maybe the ETECs are different as far as rudder/prop interference goes.

Oh, and take it out on the water in the open, toss a life preserver or bouy onto the water, and try going forward and backing around it, with the wind from different directions, stuff like that . Get a feel for what it takes to drag the stern around with the engine - without the centerboard, not so good - with the centerboard down, should be way better.

[DaveB]

Ron,
With a 9.9 hp the best top end would be around 5.5-6 knots in calm waters. The 25 inch shaft is much better suited for your boat as you will not get on plane and in rougher conditions you have less cavitation on the prop. because of the lower depth of outboard. (I would recommend the 25 inch shaft up to 30 hp) for the Mac.X or M.
With a 50hp or more, it's much diffrent, being able to get on a semi or full plane the shaft has to be 20 inches.
One thing I might add, if you have people on the bow when motering with a 20 inch shaft at 1-3 knots the engine will cavitate on small waves due to the load up forward and stearn lifting up. Only about 180 lbs person forward makes a diffrence on my boat.(you notice it when a person up in the bow ready to dock )
Dave

Our 2001 X runs a Honda 9.9 which my dealer verifies has a 25 inch (extra long) leg. It has worked perfectly in driving into 4-5 ft waves with prop staying fully immersed with no cavitation or ventilation, unlike the shorter legged Nissan 8 on my old 1988 26D.
A 20 inch leg might have less drag at planing speeds, but that is not an issue on our X because a 9.9 would not drive it beyond hull speed regardless of leg length. For us the critical requirement is reliable, efficient powering of the boat into big waves.
Ron

[ronacarme]

Dave B.....Your comments sound reasonable to me.
Incidently and not really on the point of this thread, our 2001 X in flat water....
1.when new (clean bottom) with a new 2000 Evinrude 9.9 4 str with high pitch prop at WOT would show 7.5 mph (say 6.5 kn) on the GPS...
2.now with fairly rough ablative bottom paint and a 2006 Honda 9.9 4 str with high pitch 4 blade prop at WOTshows about 7.2-7.3 mph (say about 6.3 kn) on the GPS.....
so given a bit of error on my GPS, your 9.9 speed estimate fits well with my experience.
Ron