Not so swell when it leans

[Vindicator]

have been tackling this problem for some time now. When I come down over from the back of a swell the boat wants to take a sharp left turn. It doesn't do it every time and does it in varying degrees. (scared sh!t out of the kids on sunday). It doesn't seem to matter whether I come straight over the swell or at an angle. I have noticed that the boat does lean a little to the right when on the plane and doesn't seem to make too much a difference transferring weight. I have been contemplating trim tabs but don't know whether I'm barking up the wrong tree. The boat is 6.7m alloy centre cab. Please help for the kids sake:-/

Cheers
Kezza

[snelly1971]

have been tackling this problem for some time now. When I come down over from the back of a swell the boat wants to take a sharp left turn. It doesn't do it every time and does it in varying degrees. (scared sh!t out of the kids on sunday). It doesn't seem to matter whether I come straight over the swell or at an angle. I have noticed that the boat does lean a little to the right when on the plane and doesn't seem to make too much a difference transferring weight. I have been contemplating trim tabs but don't know whether I'm barking up the wrong tree. The boat is 6.7m alloy centre cab. Please help for the kids sake:-/

Cheers
Kezza

Do you have a fin fitted to the outboard???


Mick

[Greg P]

Tabs will make the broaching worse in a following sea if used but they have far more benefits for your boat in all other conditions if you do fit them. Try playing with your outboard trim right out to keep the bow up when running downhill. That is about all you can do if you have sorted out any weight distribution on the deck. It maybe a nasty habit of the hull in that particular sea condition but I am not familiar with your hull.

[Vindicator]

Do you have a fin fitted to the outboard???


Mick


No, I haven't

[disorderly]

Do you have some photo's of the rig mate..it does look nice...and the problem you describe can, as Greg P states, sometimes be attributable to trimming the motor too far in...tends to pull the nose down and can dig in..??..

[Moonlighter]

Hi Kezza

I had a old Quintrex many years ago that did the same thing - very scary when they broach like that. But I'll never own another one of their boats, ever again, so won't have to go there again thankfully.

As Disorderly said, it can be a nasty trait of the particular boat hull that is caused or inherent in its design - I hope that's not the case because if so I don't think there's much you can do about it. In years gone by there were some brands that were notorious for this but these days with naval architects involved in many plate boat designs its much less common as a design fault.

Or it can be caused/contributed to by too much in (down) trim or too much weight forward when you are in a following sea. Try trimming out a fair way as Dis suggested, and also see if you can shift some weight down to the stern. Both should help the situation. Let us know how you go.

Best of luck

Grant

[Angla]

I will have to agree with the trim as a possible answer to the problem.... I would however hesitate and say to try just a little at first and then a little more.
If you trim up too much, you may cavitate just as the boat crests the swell.

My $0.02

Chris

[disorderly]

Hi Kezza

I had a old Quintrex many years ago that did the same thing - very scary when they broach like that. But I'll never own another one of their boats, ever again, so won't have to go there again thankfully.

As Disorderly said, it can be a nasty trait of the particular boat hull that is caused or inherent in its design - I hope that's not the case because if so I don't think there's much you can do about it. In years gone by there were some brands that were notorious for this but these days with naval architects involved in many plate boat designs its much less common as a design fault.

Or it can be caused/contributed to by too much in (down) trim or too much weight forward when you are in a following sea. Try trimming out a fair way as Dis suggested, and also see if you can shift some weight down to the stern. Both should help the situation. Let us know how you go.

Best of luck

Grant

Grant ,It was Greg P who proposed the idea's.... I just concurred http://www.ausfish.com.au/vforum/../yabbfiles/Templates/Forum/default/smiley.gif.

[Roughasguts]

Are you backing off the throttle, or increasing your speed.

If your comming of the back of a wave that say would push a surf board 12 kts and your doing 20 knots just before, then your hull is now doing 8 kts relative to the water.

So what I'm saying is the hull has fallen off the plane and it's less controlable and in the duldrums because it's only doing 8 kts relative. So what you need to do is be ready on the throttle to give her more power to gain more control over the rudder therfore steering, and control over the lean.

Aircraft land in to a head wind because you have more control.
But you land in a tail wind (eg comming of the back of a wave )and boy have you got your work cut out for you. Your going a lot faster have little control with ailerons and rudder, and if the wind speed changes chances are you stall and crash.

Same principle applies to a boat as well, Hand on the throttle any drop in controll then get ready to increase speed to gain more control imeadiately.

[Mr__Bean]

Kezza,

As mentioned by others, to prevent broaching you have got to get the nose up. Shifting weight left or right will have little benefit, move your weight down the back and trim up the nose higher than you otherwise would normally run her.

I also find it better to run a bit harder rather than slower in these conditions.

It is a trait of some larger plate ally boats, especially those with large front cabins as there is less overall weight in the boat, if the nose digs in a bit and the arse is lifted by the wave action it may come around to broach, as soon as to start to feel it go you have to stear into it.

For interest, where is your fuel tank? Do you have much weight added to the front?

- Darren

[Noelm]

broaching is a very interesting thing (and scarey as well) it can be caused by a lot of things, it can sometimes be cured, sometimes it is a "feature" and you will never be able to fully get rid of it, a simple thing like weight distribution can sometimes minimise it (as mentioned earlier) you need weight in the stern, or Motor trim to get the bow/stern trim right, you mention your Boat leans to the right when under way, it could be possible that at just the wrong time, the Boat leans, and sort of like a skate board, it just steers left because of it, seeing as it always goes the same way, appears to be a slight clue, normaly a broach prone Boat will go either way randomly, but yours always goes right, so there must be a reason, so try the easy things first, ask others with the same Boat, and then ask the Manufacturer for assistance.

[FNQCairns]

Cannot add more except even the worst boat can be driven to exclude broaching and still make good time if the person driving stays ahead of it with constant trim and often throttle work, assuming adequate power and proping.

Your trim tab might be adding to your problem at the speed the broaching becomes a factor?

Even good boats not known for it will broach with too little power on the back and/or poor proping often the better the ride of the boat the more prone it may be, never had a flat bottom punt try and broach on me.

cheers fnq

[Vindicator]

Thanks for all your replies, just to answer a few.
I usually always have the motor trimmed up on the way in.
The fuel tank is in the back half of the boat, not right at the back but in the back half.
There has been no extra weight added to the front.
I'm always ready on the steering to correct it and most times you do, just sometimes you get caught off guard.
Will try and increase speed after going over the wave, haven't yet cause I was worried we'd go over even further.
I think I'll leave the punt for the creeks.

Cheers
Kezza

[Roughasguts]

Kezza, don't think of giving the motor short bursts of power more speed.

Cause that don't initially happen, but what you get is more thrust from your prop to control the steering of the boat much better.

Low speed high thrust, means you can turn your boat a lot quicker and in a smaller radius, than you ever could at high speed.

cheers

[Vindicator]

Thanks roughasguts, now I get the point.

[ryank]

nothing can really be done to fix it. it just happens to some makes. they only way to help it is to adjust motor or put some wedges in or get rid of the fins on your motor if u have them.

[Smithy]

That day I saw you come through the mouth of the Mooloolah River was interesting to say the least. It got comments from my customers. Apart from trimming out to cavitation point and loading to the back when running home in a following sea (move the eskies to the back and get guys to sit on them), there will not be much you can do. Will be an indiosyncrisity to do with the deadrise/beam/weight distribution formula. Some boats are good downsea and others are scary.

[FNQCairns]

If it really is bad, drop the engine down (I dunno where you are ATM in any way with setup) and fit a lower perfromance prop to it, either a 3 blade of the elephant ears shape or a 4 blade (both high surface area to pitch ratio). You may need to go down in pitch to pull it off.

This will give you more muscle over your bow actually the entire boat to keep the bow up, economy will suffer over the entire trip but first go see 5 different experts and get them to look the entire rig over for anything they can find that might lead to your problem. Odds are the first blokes recommendation will be wrong and will do nothing but cost you money, work toward a consensus and then try it.

good luck

cheers fnq

[Noelm]

would still be interested to know if anyone else has the same Boat, and if theirs performs the same.

[Vindicator]

would still be interested to know if anyone else has the same Boat, and if theirs performs the same.


I'll start a new thread to find out

[Outsider1]

I would really like to see your engine set up. Can you post some piccies when you have time, the usual on height relative to the keel, prop details etc etc. I reckon there has got to be at least some fine tuning there.

I have found that the set up of my old motor vs my new is chalk and cheese. The old motor set up was a pig in the washing machine that is Morton Bay off Cleveland Point on a bad day. I wouldn't say I was every truly worried it was going to broach but it would "surf" on some of the bad stuff and it was a handful to control. The new motor setup goes through the same seas with nary a thought. A bit of trim and it is sweet.

Not saying it is going to solve your issue but there has got to be some fine-tuning to at least lessen it a bit I reckon!

Cheers

Dave