Increasing Efficiency

Are there any ways to increase the efficiency of an existing hull/engine/drive combo? I'm not talking high speed, but say in the 25 knot cruise range.
The theoretical hull would be a 30' long express cruiser, 11' beam, 24 degree deadrise, 10,000 lb displacement, twin inboard gas engines. For yuks lets assume its a 30' Searay Weekender of the 1974-1979 vintage.

I know you could change to diesels as they are more efficient then their gas counterparts, but is there any thing else you could do to the hull or driveline to dramatically increase the cruise efficiency? And possibly lessen the wake?

Add a pad bottom? Is it worth it at 25 k cruise?

Change shaft angle?

Prop tunnels?

Extended running surface of the bottom via larger, longer tabs or plates?

Shift of CG?

Decrease weight dramatically?

Ideas? Comments? Actual experiences?

Thanks,
Dennis

 

Most of the options you list are pretty drastic - except the one that IMHO is the most important - reducing weight. Now how you go about doing that depends on your situation. If you've ownde the boat for a while, chances are, that it's full of stuff that's accumulated over the years - "just in case you might need it". Other big ticket items include not filling the fuel and water to the brim when you're only nicking 'round the corner for a day cruise...
If the boat has a generator, do you really need it?
Are you carrying spares that you don't have the tools, or possibly knowledge, to fit?
etc etc....

Having said all that, I fitted a foil to the 'cav' plate on my 27' 1993 Sundancer, and it improved performance measurably - though not enormously....but that, along with bigger tabs, would probably only benefit a vessel that is overweight (I think... )

 

Some of my ideas were more radical then others I admit. But the one I've most often thought about is the addition of a pad to the bottom. I know it would be lot of work, but would be easier then say, changing the shaft angles, eh?
Has anyone ever heard of a pad being added to the bottom of an existing deep (24 degree range) vee hull? How far forward would a pad bottom need to extend? How wide a pad should/could be added to generate measurable lift? I would think that the added lift would help.
Dennis

 

Something 'Head'...

Hello...

You are asking the big questions without considering the costs or the 'pleasure factor'...

Donzi - or whatever his secratary knew him as on a first name basis - played with ride pads on the last say 10% of a 19 to 22 degree deadrise 25 foot odd hull - leading to Cigarette One...

With antihedral in the main chine - and some in the aft lifting strakes - he found the '*** tended to skid on the plate, and was a (B)itch to counter with the trim tabs'...

Sounds to me that even a cheap set of Bennet trim tabs would be the way to go - keep the full run aft - easy, fast, self levelling add on retro fit - no stuck in the parking lot talking about your ideas for 2 years while grinding out modifications to the glass work for you...

See http://www.boatshop.com.au/bennett.pdf ...

Think about the 'pleasure factor' - that grand - right hand of God equation that involves (X) work to you (Y) cost to you (Z) lot depreciation do to lack of water appreciation - and most important - (A) Wife suspicion of your intelligence - just going boating...

Next - think about what introducing a flat ride pad into an ocean slicing true deep vee (beyond 19 degrees) is - it's like a Macgregor sailboat - I want a low deadrise wakeboat with ocean going race properties - God can only slice hairs so thin...

The Physics get washed away in the ad campaigns...

Happy WD40 cleaning of your leather shoes...

SH.

 

I come to this site to pick all your brains. I'm not a designer. Just a boat nut. When you guys respond with things like "antihedral", I have to go look up what the heck your talking about. Then maybe I've learned something. Thanks.

This hasn't been my first post that has gotten some heads shaking, I'm sure, and most likely isn't my last. I guess I keep trying to think of ways to make older boats better as I just can't see spending the 100k plus it takes to buy anything new these days. I know, I know, I'd be better off and probably save money in the long run if I'd stop being cheap and bought a new or newer boat, but that's not me I guess.

My car I drive everyday is a 1967 Chevelle Malibu convertible that I swapped a 1999 Corvette LS1 into, ECM, fuel injection, catalytic convertors, electronic transmission and all. Couldn't find a car I liked so I built it. It gets 25-26 MPG and is so reliable I let my teenage daughter take it anywhere. Smooth and quiet, too.

Just FYI, I don't own the theoretical Searay I described earlier, but I do like the style of the boat. The problem is the ones I've seen, with trim tabs, all plow through the water with their bow in the air leaving a wall of water 3' high behind them. Seems to be typical of mid size express cruisers of the era.

I boat in the California Delta which is made up of miles of narrow channels. I would hate to become one of those people that motor though the area with no regard for what my wake does to the millions of small ski boats, etc, that populate the delta. I have a ski boat now and I get tossed by those inconsiderate people way to often.

So why can't we (meaning you) figure out a way to make old boats perform better? Will I make money at this? Surely not. I could have bought a new Corvette for what I have in my Chevelle. But there have been vast improvements in boats since the late 70's, and it wasn't all engine improvements. Hulls are more efficient, props are more efficient, etc. With everything that's been learned in the last 25 years, there must be ways to improve older vessels.

Will they ever perform like new Fountains? No. Will they have the beautiful lines of Hinckley picnic boat? No. But I enjoy the research and maybe someday I'll enjoy the project.

To some it all up, I'd be interested to hear what others think or about things that you've tried. Good or bad, pro or con. Tell me what you think, you won't hurt my feelings.

And in return I promise I won't ask any of you to chip in to my bottomless pit.

Dennis

 

On your sour note I wil just opt out - best of...

SH.

 

Tongue in Cheek...

Hello...

I am just suppositioning (not a real word) that you did not pick up on the rather broad and historical verbative and reference that can only be clawed against old Donzi...

If I have offended you in any way, well then I must apologise, but only for yourself...

Good luck in your pursuit of both a historical or a technical answer, or discussion, to your question - plenty of reference in any library employing the Dewie Decimal System...

Best of...

Nice to have read your bit of puss - up, and lip...

SH.

 

Hey Sean, good to see/read you again. Still in BC I see.

On the deep V boat question:

Since LSI wants to drive his boat in the narrow channels of the Delta area, a deep V is just the wrong kind of boat to mess with in the first place. The comments about its inefficiency are well taken and should give a clue that there is some waterworld where the big wake and other bad habits of the type can be excused. That place is where you want a monohull (single hull, LSI) to run fast in open water with waves. In every other place, there is some other hull type that is better for the purpose.

LSI is just trying to start at the wrong place to get where he wants. Much better to look at boats with low deadrise and lighter weight for lower wake and better efficiency with enough sharpness to the forward sections to handle the expected wave action that the boat will see.

I never heard of antihedral either but its meaning is obvious. In aircraft it is called cathedral for down sweeping wings and dihedral for the more normal upsweeping wings.

And LSI, you can either look for the hidden meanings in Sean's writing or just get on with your life.

 

Ok, for starter's, Tom, as usual is spot on - a deep vee go-fast is probably not the boat for this application. But then, I can be pretty sure that your theoretical Searay has a transom deadrise closer to 17 degrees (as mine did). And whilst this may still be somewhat deeper than necessay for your area - I don't know, living on the other side of the world as I do... , but I reckon you'd be hard pressed to find a better production built, better equipped and easier to find boat for the money.
Also, there are two main reasons why you see most boats - and I would contend that this isn't restricted to express cruisers - wallowing along with their bums dragging an enormous wake:
1. Their ignorant owners fill them with junk so they're too heavy to run correctly &,
2. Their ignorant owners drive them at speeds that are two slow (or too fast depending on how you look at it.. . At 16 knots, my Searay was a pig, but a 22 it ran with minimal trim and it's wake was halved......

 

Meaning Me - then...

OK - now that I have a clear head - and before I start getting paranoid...

Antihedral is the reverse of dihedral - like an F4 Phantoms tail end - OK so Tom prefers cathedral - that's fine - I like whisky more than wine - sounds a bit Country...

Right - so - lifting strakes are the little nubs that run from the bow to the stern - you know what a chine is - these things are not spray rails they are there to provide a flat to the waters surface to lift the hull free of its bow wave - a lot of folks stick some downturning antihedral into same to create a tunnel effect and to provide some bite in hard turns at speed...

So the bow wave - is what you see those guys pushing around while at displacement speeds - un trimmed - see most deep vee production boats are all engine - but when they operate at planing speeds and climb over their bow wave and are trimmed out level all things are good in the world - trouble is most Joe's don't get the training...

If you want to reduce wash at displacement speeds you can change the horizontal trim by having a water tank with pumps as far forward to affect trim - it can even be a part of a two tank fresh water system - while planing trim tabs are a neccessity really - as to reducing wake in a fast deep vee - it's just not in the physics...

As for ride pads - most modern manufacturers end the inboard strake a few feet before the transom edge to provide same - however the upper strake usually runs full aft - to try and prevent water from running up and off the 'running hull' - killing lift...

If you can find it - I think it's out of print - go get Power Boat - The Quest for Speed Over Water - by Keving Desmond - It describes just about every idea that has been tried since Fulton...

Also The Hydrodynamics of Planing Craft....

Limited start at http://www.bruceroberts.com/public/HTML/POWERBOAT_DESIGN.htm

I am going to upload one of my older boats - just because I figured out how to - http://www.boatdesign.net/forums/attachment.php?attachmentid=1308

SH.

 

I'm with you most of the way Sean, but I have to differ on one point. Adding weight to the bow of a planing-hulled craft which is travelling at intermediate speeds will not have an enormous effect of the wake.
By that I mean that if you have a 25ft LWL then you dislplacement speed is around 6.7 knots. Running around at 10 or 12, as you so often see some twits doing, will create an enormous wake, regardless of the trim of the vessel. The only way to really deal with it is to slow down - or speed up.

.....now, now...Tom, before you leap into keyboard action, I'm talking about relatively heavy, deepish vee hullforms here - not boats like Liz - elegant, lightweight shapes that can produce virtually no wake almost regardless of speed

 

Yeah your'e right - remember most times that I am not working I am drinking - leads to many sidetracks - won't effect your wash much - but will improve visibility sometimes if tabs won't lower the bow...

It does have the effect though of presenting a more designed line to the water surface - ie: most designers - well ALL designers don't envision their boats bow up 15 degrees and acting like a plow at any speed...

And yes I am talking heavier offshore Vees - not open bowriders where you can move people around to the same effect...

The boats we put tanks into would drain manually when at speed and fill same to trim the bow down at slower speeds when the tabs became ineffective at doing so...

Time for a drink...

SH.