Stable cruising speed?

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bobbob
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Stable cruising speed?

Post by bobbob » Mon Jun 20, 2016 1:25 pm

This weekend I had a chance to try out cruising at WOT with ballast in and out for extended periods over different water conditions. I have an :macx: with Merc 60HP.

On the way out, water was very calm and very little wind so I dropped ballast and was able to get up to 17 kts SOG (as measured by GPS). I found that it was pretty easy to track a constant heading and steering was reasonably responsive, however I needed to be on close lookout for wakes produced by passing motorboats because with ballast out you are thrown from side to side pretty easily.

On the way back, wind speed was 5-10kts and coming from starboard. Water was a little choppy but no swell, but I decided to fill ballast anyways. I was able to get up to 14 kts SOG (again, GPS measured). I found in this configuration it was difficult to keep a straight heading. The boat kept turning to starboard and I would have to course correct, and the steering was much stiffer when I needed to do so meaning it was too easy to overcompensate. I'm not sure if this was because of the amount of freeboard presenting itself to the perpendicular wind, or because the boat was still in an unstable "semi-plane" mode.

Thoughts?

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Signaleer
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Re: Stable cruising speed?

Post by Signaleer » Mon Jun 20, 2016 3:13 pm

I have the :macx: as well, with a Merc 90hp Saltwater 2-stroke.

Ballast in, mast on, calm to calm-ish water I can get to 18.25 knots or 21 mph with just me. This is with just me.

Ballast out, no mast, same conditions, I have hit 27 mph or 23.5 knots. This was with me and a light passenger.

The handling is definitely different and something to get used to. I have a tendency to pull to starboard, but I thought this was due to the prop-torque? I would love to get an opinion on this.

And although I think the :macx: is an awesome boat to motor on, it is simply not as 'locked in' as other motor boats I've been on? I don't know exactly why, but it seems to kinda 'skid' along the water, which if there is a wind on the beam, seems to blow more to the lee than I'm used to on other boats.

I'm interested in other's experiences and opinions as well!

Ed

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Tomfoolery
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Re: Stable cruising speed?

Post by Tomfoolery » Mon Jun 20, 2016 3:40 pm

Signaleer wrote:I have a tendency to pull to starboard, but I thought this was due to the prop-torque? I would love to get an opinion on this.
Have you adjusted the trim tab/anode to neutralize some of that?

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Signaleer
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Re: Stable cruising speed?

Post by Signaleer » Mon Jun 20, 2016 4:51 pm

Tomfoolery wrote:
Signaleer wrote:I have a tendency to pull to starboard, but I thought this was due to the prop-torque? I would love to get an opinion on this.
Have you adjusted the trim tab/anode to neutralize some of that?
A prerequisite to answering this would be understanding what the hull you are talking about! :)

I'd love to do whatever you tell me to do, but I'll need a bit more description!

Ed

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Deeseas
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Re: Stable cruising speed?

Post by Deeseas » Mon Jun 20, 2016 6:46 pm

The sacrificial anode under the cavitation plate can be adjusted to help with prop pull.
Doug

DaveC426913
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Re: Stable cruising speed?

Post by DaveC426913 » Mon Jun 20, 2016 6:55 pm

Signaleer wrote:
Tomfoolery wrote:
Signaleer wrote:I have a tendency to pull to starboard, but I thought this was due to the prop-torque? I would love to get an opinion on this.
Have you adjusted the trim tab/anode to neutralize some of that?
A prerequisite to answering this would be understanding what the hull you are talking about! :)

I'd love to do whatever you tell me to do, but I'll need a bit more description!

Ed
A pic's worth a thousand cuss words. :D

Image

DaveC426913
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Re: Stable cruising speed?

Post by DaveC426913 » Mon Jun 20, 2016 6:57 pm

bobbob wrote:I found in this configuration it was difficult to keep a straight heading. The boat kept turning to starboard and I would have to course correct, and the steering was much stiffer when I needed to do so meaning it was too easy to overcompensate. I'm not sure if this was because of the amount of freeboard presenting itself to the perpendicular wind, or because the boat was still in an unstable "semi-plane" mode.

Thoughts?
My :macx: is hard to keep straight below 7 knots. I fight with it or it will wander to port and starboard. I have to get above 8 or so before it'll settle down.

One of the things I've been practising when alone is seeing if I can minimise the drift by standing at the helm and shifting my weight rther than turning the wheel. Kind of a pain though.

bobbob
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Re: Stable cruising speed?

Post by bobbob » Mon Jun 20, 2016 8:05 pm

DaveC426913 wrote: My :macx: is hard to keep straight below 7 knots. I fight with it or it will wander to port and starboard. I have to get above 8 or so before it'll settle down.

One of the things I've been practising when alone is seeing if I can minimise the drift by standing at the helm and shifting my weight rther than turning the wheel. Kind of a pain though.
Wow, that is really interesting, and completely opposite to my experience. 7 knots is basically hull speed and I find it completely stable. From 8-12 is the range I find wildly unstable.

I don't find my motor consistently pulls to starboard so I don't think the trim tab needs adjusting. It just seemed to me when I would fall off course it would generally be to starboard.

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sailboatmike
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Re: Stable cruising speed?

Post by sailboatmike » Mon Jun 20, 2016 9:32 pm

I find a tendency to jump to starboard at transition speed between displacement and planing speeds around 10knts especially is weight is moved around like someone walking from one side of the cabin to the other

bobbob
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Re: Stable cruising speed?

Post by bobbob » Wed Jun 22, 2016 2:43 pm

The other half of this problem is my stiff steering - I suspect the problem would be much more manageable if I upgraded it.

Am I correct that the Uflex Rotech system is easily drop in replaceable for the 96X stock system? And I should have no problems with my Raymarine autohelm?

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Don T
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Re: Stable cruising speed?

Post by Don T » Wed Jun 22, 2016 3:28 pm

Hello,
Yes the U-Flex system fits perfectly and works great.

Don T

bobbob
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Re: Stable cruising speed?

Post by bobbob » Thu Jun 23, 2016 8:43 am

Thanks. Can I assume this is a straightforward swap then? ie. no need to remove the steering wheel, no need to cut new or wider holes anywhere, etc.

If not, would I get most of the same improvement just with a new steering cable? I'm willing to live with the slop in the existing system, it just needs to be substantially easier to turn.

Thanks!

sandpointsailor
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Re: Stable cruising speed?

Post by sandpointsailor » Fri Sep 02, 2016 11:58 pm

Code: Select all

I think I am having a similar problem with power handling on my 26M.  I have a 40 hp Suzuki.  When running with full ballast and 2 people, and mast raised, I am having a hard time keeping a straight course when I am at about 5 to 6 knots.  Am I in a transition zone between plane and displacement that is inherently unstable or do I need to adjust the trim tab?  If so, how do I do this?  What speed are others achieving with this motor and configuration?  I may have been too chicken to really crank it up.  I have been typically running about 4000 rpm and keeping it to under 6 knots.  I recently learned from the dealer that these motors can easily handle 6000 rpm.  And lastly, does anybody know the optimal rpm or boat speed for best fuel efficiency when powering. thanks folks!

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Whipsyjac
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Re: Stable cruising speed?

Post by Whipsyjac » Sat Sep 03, 2016 11:54 am

1. below hull speed.always have at least some center board or dagger and one or both rudders. Unlike power boats there are no hard chines or skegs on your hull to help you track at low speed.

2. These boats are meant to plane bow high, trying to trim the bow down is detrimental to handling on plane.

3. When planing the engine trim will affect steering balance. I learned through trial, error, and near mishap. If your boat steers to port normal but turns hard to starboard with minimal steering input raise your motor trim until your boat turns both ways equally. If you require excessive up trim(prop ventilates, you begin to lose speed, or steering immediately shifts to too much port) then you may need to realign the trim tab behind the prop.

I hope this helps.

Willy

PS when switching to Roto-tech I had to remove the wheel. I am quite happy with it though. http://www.macgregorsailors.com/forum/v ... ng#p269663

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