Adding more chain- will it help?

T

tobnpr

New Member
Nov 12, 2006
3,246
New Port Richey, Florida
Boat Info
1988 300 DA
Engines
tw 350's w/ Alphas
I need to run with full tabs all the time. I think the 39EC was really designed around the gassers, and the extra weight of the diesels kills the running attitude of the boat. Without tabs- even at cruise- the bow points skyward and the stern digs a hole...and cruising speed drops from 23 knots to 21.

My first instinct is that adding weight to a boat is never a good thing, but I was wondering if adding a few hundred pounds of chain rode might help by lowering the bow, and maybe eliminating the need for the tabs, which increase drag.

So my thinking is: Could adding extra weight at the bow offset the need for trim tabs- and make the boat run faster, despite the added weight? Anyone have experience with this?
 
I have the same problem as you minus the diesel engines. My anchor rode is all rope (Good Windlass), but my fresh water tank is in the bow, all 100 gallons of it. I choose to run with as little water in that tank as possible at all times and I've tried it both ways (near full and near empty). The boat's giddy-up is remarkably greater without the 7lbs/gallon up there. I'd forego with the chain - from my experience, the drag caused by tabs is less detrimental to economy and ride level than carrying the extra weight.

Of course my gas engines will bitch more about added weight than your diesels.

Where is your fresh water tank? If it's in the bow, maybe you can experiment with weight using water and then come to a decision about carrying extra chain.
 
I've never been on a boat like yours but if you have the typical v-berth get some of your big buddies on it and experiment. That doesn't sound right but you know what I mean.
 
The 460DA is generally known as a bit of a tail heavy boat so one of the first things I did was to change to an all chain rode, 180' of 5/16". Since I didn't have much experience running with nylon rode, I cannot comment on the difference, only that I had the same concerns initially. I still use some tab at cruise but not a lot. Boat runs as in the photo below and that's with the dinghy on the platform.

James
 
A friend of mine that purchased a brand new 39 EC with diesels in 1990. He told me that it came through from the dealer with 200 ft of anchor chain. He used to fight untangling it all the time! Hope it helps. Bill
 
I'm curious about the tangling. Each boat I've had used 180-200' of chain with never a problem. Chain always deployed easily. Old three strand rode certainly tangles and it's one of the reasons that I have gone with chain (aside from the rocky seafloor).
 
Having owned a 390 before, although one with gas engines, as well as having a lot of time on several different Sea Rays, I honestly believe your nose high attitude is the result of the thrust angle on the 39EC. This boat has full prop pockets yet she only draws 28" or so and that means it has to have a shallow thrust angle. A shallow thrust angle means reduced lift and a dug in stern. If I were gambling on a fix, I'd take a had look at longer or wider tabs before I increased the weight of the bow.
 
Mike,

I got to go along with Frank. I would put the largest tabs I could fit on there.

I had thought about changing mine and going to twin cylinders. Mine looks at the sky w/o tabs but does well with full tab.

If you wanted to play with it bring 5~6 80 lb bags of Sakrete home and get your guys to put it down in the master and go for a run. If it works you could put in the nose under the bed.

I still like the big tab idea. Call Bennet. I'm sure they have some ideas.
 
fwebster said:
Having owned a 390 before, although one with gas engines, as well as having a lot of time on several different Sea Rays, I honestly believe your nose high attitude is the result of the thrust angle on the 39EC. This boat has full prop pockets yet she only draws 28" or so and that means it has to have a shallow thrust angle. A shallow thrust angle means reduced lift and a dug in stern. If I were gambling on a fix, I'd take a had look at longer or wider tabs before I increased the weight of the bow.
Click to expand...

Ahhh...yes, I get it now- a more pronounced driveshaft angle would tend to force the bow down.
My tabs extend from the chine to the prop pockets, so wider isn't an option:
2007_1112Josea070003.jpg


But, I could increase the surface area by going with wider tabs, I think the ones on there are 9", I could go to 12"...great idea, I'll talk to Bennett and see what they suggest. Thanks!

Mike
 
Woody said:
I've never been on a boat like yours but if you have the typical v-berth get some of your big buddies on it and experiment. That doesn't sound right but you know what I mean.
Click to expand...

So, how DID you get your nickname? : )
 
It may just be a matter of semantics, but I think the issue is adding stern lift to get the rear of the boat up and out of the water...which is why I don't think adding weight to the bow is going to do much more than slow you down.

Another observation after seeing the pix of your 39 out of the water is that if you ever find the need to re-prop the boat consider going to as large a diameter 4 bladed props, and you may already be there on the diameter.........get the tips too close to the hull and you buy ventilation problems. 4-bladed props will have less pitch per blade and that means less slippage per revolution which should translate to more efficient power delivery. Most people who make that change notice a lot of difference as their boats come up on plane and that benefit gradually diminishes as speed increases, but most notice 1-2 kts gain @ WOT. Every little bit you do to decrease drag, increase lift and improve efficiency will help your lift issue.
 
Thanks for the suggestion, Frank. I'd wondered if 4-blades might help; makes a lot of sense. I'll be hauling for a bottom job in a few months- I'll discuss it with the prop shop.
 
Frank
What's the trade off with 4 bladers. Doesn't something suffer? Hole shot, top end, cruise speed? If it's a perfect solution, why don't they make the standard on all of these pocketed SRs?

This calls to mind something I've always wondered about (while we're on the topic of underwater gear), why does SR use such tiny little rudders. Mine don't even extend to the full draft of the props. Less drag?
 
Its an expensive change.........one I wouldn't make unless you found a deal on eBay or were forced to shop for props because the bottom jumped up and bit you.

RON - I think cost is the down side. The guy that bought my 39 had to repower it shortly after he bought it (Not my fault!) and went to EFI engines and Z-F gears with a different ratio final drive. He put 4 bladed props on where I just had 3 blades........the difference was huge on the bottom end gradually changing little effect on the top end other than smoothness and 1.5 kts.
 
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fwebster said:
Its an expensive change.........one I wouldn't make unless you found a deal on eBay or were forced to shop for props because the bottom jumped up and bit you.

RON - I think cost is the down side. The guy that bought my 39 had to repower it shortly after he bought it (Not my fault!) and went to EFI engines and Z-F gears with a different ratio final drive. He put 4 bladed props on where I just had 3 blades........the difference was huge on the bottom end gradually changing little effect on the top end other than smoothness and 1.5 kts.
Click to expand...

Ruh Roh...more temptations.:smt021
 
So with my fat bottomed girl, what would I expect if I went from 20x20 cupped 3 bladers to 4s? More speed (cruise and top end), more efficiency, better docking manners, flatter running angle, better hole shot.

Maybe I'll do an insurance job on my props and "hit something!" ;-)

Can I get bigger rudders too?
 
tobnpr said:
Ahhh...yes, I get it now- a more pronounced driveshaft angle would tend to force the bow down.
My tabs extend from the chine to the prop pockets, so wider isn't an option:
2007_1112Josea070003.jpg


But, I could increase the surface area by going with wider tabs, I think the ones on there are 9", I could go to 12"...great idea, I'll talk to Bennett and see what they suggest. Thanks!

Mike
Click to expand...

Bennett sold me 12" Trim Tabs same width for my 34 da, what a difference, planes at a slower speed, bow comes down, better visibility. It works!:smt038 not a big deal or big expense, easy to replace. I changed them in 02, costs $228.25 including shipping.
 
Listen to us..."Hole Shot"..."Top End"...you would think that we had something that would "run".:thumbsup:
 
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Yeah, like we have one of these...:lol:

061101_SpeedBoat_hmed_2p.hmedium.jpg
 
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