Higher reduction (more torque) allows a larger footprint (prop) which gives far better low speed maneuverability and hole shot (take off). It also adds additional drag to some degree so it comes with a bit of a trade off as far as top speed goes if that makes any sense.

 

Hi Joe C....

I'm sorry I can't help you with the gear reduction question but I want to give you a couple of things to think about. Your old 34' Flybridge weighed about 12,000 lbs. The listed dry weight of the 410AC is almost double that at 23,000 lbs. Add 2,000 for fuel and another 800 for water then add gear and humans you're going to be pushing over 26,000 lbs.

Boat engines are more about torque than horses when it comes to moving weight and mass. A few years ago I looked very hard at a beautiful 1990 440AC (same boat) with stock 340 HP big blocks. The boat was immaculate but after a couple test rides I knew that I would never be happy with that boat with gas engines....no matter what modifications were made. That much boat really needs diesels. In fact, Cat 3208s were the engine option for that boat....and it needs them. You're talking about some fairly expensive engine modifications as well as gear changes and maybe even transmissions. Then if you add bigger props, you may need bigger shafts as well. I'm betting the current shafts are only 1". That means changes in shaft logs and maybe struts....who knows?

What I'm trying to suggest here is to really think hard about this modification. You could probably find a couple of 375HP 3208s to put in but then again you would be changing props, struts, shafts, transmissions and genny.

Remember, the most cost effective way to make a boat go faster is to buy a faster boat. Good luck with your decision.

Shawn

 

Hi Joe C....

I'm sorry I can't help you with the gear reduction question but I want to give you a couple of things to think about. Your old 34' Flybridge weighed about 12,000 lbs. The listed dry weight of the 410AC is almost double that at 23,000 lbs. Add 2,000 for fuel and another 800 for water then add gear and humans you're going to be pushing over 26,000 lbs.

Boat engines are more about torque than horses when it comes to moving weight and mass. A few years ago I looked very hard at a beautiful 1990 440AC (same boat) with stock 340 HP big blocks. The boat was immaculate but after a couple test rides I knew that I would never be happy with that boat with gas engines....no matter what modifications were made. That much boat really needs diesels. In fact, Cat 3208s were the engine option for that boat....and it needs them. You're talking about some fairly expensive engine modifications as well as gear changes and maybe even transmissions. Then if you add bigger props, you may need bigger shafts as well. I'm betting the current shafts are only 1". That means changes in shaft logs and maybe struts....who knows?

What I'm trying to suggest here is to really think hard about this modification. You could probably find a couple of 375HP 3208s to put in but then again you would be changing props, struts, shafts, transmissions and genny.

Remember, the most cost effective way to make a boat go faster is to buy a faster boat. Good luck with your decision.

Shawn

My shafts are 1 3/4 and I'm spinning 24 inch 3 blade wheels. I understand the difference between torque and HP. It was described this way a log time ago to me, torque gets you up to speed HP keeps you there. As for diesels I would not consider 3208 cats as they were dogs! I had 2 friends with them one in a 42 Sundancer he makes 21 knots at wot. The cat 3196 would be a better choice but it's bigger and heavier the the same HP in a Cummins. The QSC diesels sound like gas engines as well. I love this boat so spending the money on it isn't the problem. Diesels would be the better option but I think I can get this boat to do what I want with gas for now. I've seen some 55 sea rays with the twin 900 hp option diesels getting 28 knots. They weigh 56,000 pounds. Soooooo I know it can be done.

 

Which old Sea Ray did you repower? I can see the Sorento making 3 knots but not the 340 Sedan Bridge. To get a twenty five knot cruise you would need to install 40hp Cumins diesels in the 410AC. Not worth the 100k investment I would think.

 

My 34 sedan bridge did hit 30 knots with the stock 340 mercruisers. I went with 420 to 450 hp rebuilds but the boat was damaged by the marina and hasn't seen the water since. My prop/speed calculator says it should do 38knots at 5500 rpm. (Yes the 454 have the better rods to spin at 5500).

 

look into 496's or 502's (or maybe even 540's) through someone like Michigan motors......call them and tell them what your trying to do......I bet they can help - if its repower time anyway, an upgrade certainly makes sense.......you could also look at Duramax conversions (there are a couple of companies that specialize in marinizing them) but I would think any diesel conversion would be huge $$$$

 

I saw mercury racing makes a 1350 HP racing engine. It's super expensive like $200,000 each but I bet that would make my 410 go!

 

I've seen some 55 sea rays with the twin 900 hp option diesels getting 28 knots. They weigh 56,000 pounds. Soooooo I know it can be done.

My 550 Sedan Bridge has 580hp Cat 3406C's and hits 31.3 kts at WOT. But that has little to do with the boat you're looking at.

My advice: Unless you have a LOT of money that is just burning a hole in your pocket, why would you even consider spending $100,000 on a boat that is already 31 years old and not worth that much to begin with. You might just as well stand on a street corner thrown $100 bills down the sewer. The return that is going to be about the same as the return you'd expect out of your repowered 31 year old boat.

My advice #2: Don't bother with repowering. That that money and trade your old boat in on a newer one that is equipped with engines you'll be happy with.

 

I have thought about that. I don't look at my boat as an investment. I take to heart the meaning of boat, Break Out An Other Thousand. Lol. I have considered a newer boat but don't like the layouts. Since we are live aboards we take the layout and interior comforts very seriously. The 420ac is very nice looking but doesn't compare with the comfort we have on ours. The only option I see is the 65 cockpit motor yacht. Only 12 were made. It's my dream boat!

 

There's for sale on yacht trader

 

Joe,

First I take a bit of offense (kind of) at your comment that the Cat 3208s are dogs. True, they are not fast but they weren't built to be....most diesels aren't The 3208 was built to be durable and they are....unless you have the 425HP versions. I had the 375HP models in my 1984, 52' KhaShing CPMY. That boat weighed 48,000 lbs. I didn't buy that boat to go fast. I bought it to cruise offshore on the West Coast. I wanted comfortable and dependable. She was stabilized with a 3 year old Raymarine navigation system that the previous owner spent $30k on.

My next question....What's the rush? I understand wanting the space for a live aboard but honestly, if you are looking for a boat as a home there are a LOT of boats that are better suited for that task than a Sea Ray....44' or 65'. I bought the boat mentioned above to live on and cruise for 5 years. Going fast never entered the equation. Comfort, dependability, stability, convenience, space, real furniture, a galley big enough for more than 2 people.... These were what was important to me at the time.

Big boats mean big weight and mass. That means diesels to move that weight and mass efficiently....and it doesn't mean fast. It means 10-12 kts at cruise and maybe 20 WOT when you need to get out of the slop quickly. Boating forums, including this one are filled with people wanting their boat to go faster. There is no cost effective way to accomplish that. The rule of thumb I've heard is about $1000/MPH. Yep, wanna go 5 miles per hour faster? Gonna cost you 5 boat units. Re-read post #9 from Go First Class. His response is spot on.

Lastly, if you want a comfortable live aboard why not look around at some other boats. When I was looking, and I've had Sea Rays all my life, I looked at Ocean Alexander. A very well built and solid boat. They have a very nice 44' Aft-cabin, cockpit model. They also made a very nice Pilothouse model in the 50' range. You said you don't like the layouts of the newer boats so look at the mid 90's of other manufacturers. Even the bigger Bayliners (I know, go ahead and laugh) from 46' and up would be better, as far as livability. Then go buy a 22' or 27' mid-80s Sea Ray Pachanga and put your 496s of 502s in that for you speed fix.

Of course, all of this is just my opinion and you will do whatever you want anyway. Good luck. I hope it all works out for you.

Shawn

 

Big boats mean big weight and mass. That means diesels to move that weight and mass efficiently....and it doesn't mean fast. It means 10-12 kts at cruise and maybe 20 WOT when you need to get out of the slop quickly. Boating forums, including this one are filled with people wanting their boat to go faster. There is no cost effective way to accomplish that. The rule of thumb I've heard is about $1000/MPH. Yep, wanna go 5 miles per hour faster? Gonna cost you 5 boat units. Re-read post #9 from Go First Class. His response is spot on.
Shawn

Or in my case with 3406's in a 60,000 pound boat, I can easily cruise at 17kts-22kts with a WOT of 30+kts. But at WOT I'm burning 65GPH....not something I ever do for more than a few minutes to "blow out the smoke".

I generally agree with what you said. There are exceptions to the "rules" about diesels, but you're dead on with your comments about diesels being created to push big loads at moderate speeds.

 

Nice boat NorCal other than the need for some upgrades mostly in electronics. At the Newport Boat Show last week I found a different "lottery" boat than the previous Sabre 48 Express. It is now the Zeelander Fifty Five. At 3.2 mil it will remain the ultimate "lottery" boat.

 

Beautiful boat! Hope you get her one day soon. Price isn't too bad. Just out of reach for me though. I hate having a loan on my boat so I can't dream more than I have. Lol. But if I won the lottery that would solve my problem. I think I would have to buy my marina though cause I need the slips for storage. Just a thought....
I always seem to go back to the 80's and 90's with sea ray because after 2000 they started using the European design and it isn't as attractive or Sea worthy without the bow flair needed for heavier weather. Since I like to travel by boat I can see the need for this. The 65 cockpit motor yacht http://www.yachtworld.com/boats/199.../Sea-Ray-650-Cockpit-Motor-Yacht-2951979/Stockton/CA/United-States#.WcZpY0EpCEc
Will always be my favorite but only early 90's version. The newer they got the more European it became. Today it's not the same boat inside or outside.