Dorado 30 High speed stability

[Mr Efficiency]

I can't comment much more, I'd like to see the lines plan of the boat, but that won't be available, boats can look as if they are a warped plane bottom, but that one isn't, strictly speaking. I think your weight is too far aft, and the boat is riding mainly on that curved bottom well aft, acting like a "spoon" bow, which are notorious for wandering, add that to a long pod and two legs taking the CLR further aft, you have a steering effect. One possibility, would be to deepen your centre skeg, maximum at around a third of the way forward from the stern, that will move the CLR forward a bit, but not become an issue to make the boat broach in following seas. The problem there, would likely be with getting the boat on and off the trailer.

 

[Austin]

I appreciate all the help!
Going to try moving some weight forward and raising the engines to start.

 

[Mr Efficiency]

That's probably a good start, as it doesn't involve huge difficulty. I think those short videos you posted helped expand the picture of what is going on.

 

[Alexander Peter Bromley]

Did you come right with shifting your onboard weights more forward?

I would have also said the cheapest solution would be to shift weight forward so your hull is riding on the sharper end of your V.

 

[gonzo]

Is it a distortion on the photo, or are those trim tabs bent into a curved surface?

 

[JayTee]

Some additional information that may be helpful: I have a Dorado 30 but I still have the inboard diesel with a jackshaft/outdrive. Even with the engine in the middle as "designed" it is fairly squirrelly above 28 mph. Given the flat/semi-rounded stern, if feels like trying to power a high speed soup bowl. I use tabs to get the bow down so that it will help track straighter. I am not sure that Austin's issues are related to his engine heights, etc. If extending the keel would benefit the tracking without affecting steering too much I'd be interested in modifying mine too.

 

[Austin]

I have moved weight forward and raised the engines one hole but still the boat does not like to go much more than ~28-30 without getting very loose.

I’ve been doing a lot of searching to find similar hull shapes that preform better at higher speeds. Albery Brothers Boats has a similar Hull shape and they run an extended keel almost all the way aft, as well as a full length single lifting strake.

I’m not sure which one helps more, but I think I may test an extended keel on the dorado to see if they’re is any improvement.

 

[Austin]

Another Picture if an Albury

 

[Austin]

Also if it would help I can draw the hull shape in CAD just not sure what format y’all prefer.

 

[Mr Efficiency]

That boat you have supplied photos of, isn't really an analogue of your boat. It is a relatively straight sectioned vee, yours distinctly rounded, aft. That single outboard version of your boat, you provided a short video of, what is the handling report for it ?

 

[Austin]

He says the boat handles great until you try and push over 30 then it’s a handful. He likes to cruise below those speeds. Pretty much every owner of this hull I have talked to agrees they don’t handle well over 30 mph unless it’s perfectly calm out.

The reason I purchased this hull was for its fuel efficiency and it’s relatively low draft, knowing it was not designed for speed. But I would like to explore any possibilities there are to improve the hull.

I have seen threads where older commercial style fishing boats, similar to ours, where modified to handle more power and speed. I am a mechanical engineer but know nothing about hull design, I have looked into CFD testing for boat hulls but could not find anything reasonably priced.

Thus I am here to talk to experts in the field and hopefully learn a thing or two. I really appreciate all the help.

 

[Mr Efficiency]

I would say that the difference between a hull that can handle 25 mph on the open sea, and one that can handle even 35 mph, is huge. If only because ballistic trajectory starts to come into play. The aft bottom of your boat has 25 mph written all over it. I assume you want to get some extra speed when conditions allow, the only solution may be an autopilot to get rid of the weaving, but you could try the centreline "keel" idea, but I'd taper it to nothing at the transom, from maybe 4 feet ahead of the transom. Even 3 inches depth may make the difference, but it is a bit of a job to fit, and also to be sure it still rolls on and off the trailer OK. I'd certainly try that ahead of side strakes.

 

[Austin]

Just wanted to update the thread, I raised the engines one hole and did some testing and found the boat handles best when my Suzuki gauges read ~20% engine trim up.
The hull doesn't get loose till about 36 mph in choppy water but cruises well in the 30 to 32 range. The only draw back so far is the props will sometimes capitate coming down a big roller, which might be more of a prop issue.

 

[gonzo]

The propellers ventilate, because they are too far up for the amount of pitching.

 

[Mr Efficiency]

So, has the handling improved, with changes made?