HP vs. cubic inches & drive type

KD4UPL

Senior Chief Petty Officer
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Feb 13, 2010
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I'm looking for a replacement to my '97Larson 206Sei with 5.7 and a 2 barrel. It's supposedly 210 HP which I will describe as barely adequate.
I'm looking at upgrading to a Sea Ray 220 or 240 Sundeck, Chapparal 233 Sunesta, Four Winns 234 Funship, or something else similar.
I will sometimes have as many as 12 people on board, total weight about 1,600 pounds (includes 4 little kids and 3 skinny women)
I see lots of boats powered by a 260HP 5.0 which doesn't seem like much of an upgrade in HP from what I have considering the additional weight of the larger boat. I also would guess that a 5.0 would generate less torque than a 5.7. Nobody talks about torque much in relation to boats engines. Why is that?
Some slightly older boats come with a 250 HP 5.7. Which would theoretically be better a 260 HP 5.0 or a 250 HP 5.7?
Really I think I'd like the 350 Mag. which makes 300 HP. I understand that 300 HP is right at the upper limit of an Alpha drive. Would this be a problem? Are the weight, size, and power requirements of what I'm describing such that the Bravo 3 is almost "mandatory" for satisfactory performance?
If anyone has any of the aforementioned boats or one similar I'd love to hear what drive package you have and how you like it.

Thanks,
 

Streffpilot

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Aug 22, 2012
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The reason no-one really talks torque is that (torque x rpm = HP). You can have all the torque in the world (for instance, an electric motor can even make gobs of torque at 0 rpm) but without the rpm, you won't be going anywhere. The torque at rpm is what makes HP, therefore, HP is what you need to measure for your application.
 

Bondo

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I'm looking for a replacement to my '97Larson 206Sei with 5.7 and a 2 barrel. It's supposedly 210 HP which I will describe as barely adequate.
I'm looking at upgrading to a Sea Ray 220 or 240 Sundeck, Chapparal 233 Sunesta, Four Winns 234 Funship, or something else similar.
I will sometimes have as many as 12 people on board, total weight about 1,600 pounds (includes 4 little kids and 3 skinny women)
I see lots of boats powered by a 260HP 5.0 which doesn't seem like much of an upgrade in HP from what I have considering the additional weight of the larger boat. I also would guess that a 5.0 would generate less torque than a 5.7. Nobody talks about torque much in relation to boats engines. Why is that?
Some slightly older boats come with a 250 HP 5.7. Which would theoretically be better a 260 HP 5.0 or a 250 HP 5.7?
Really I think I'd like the 350 Mag. which makes 300 HP. I understand that 300 HP is right at the upper limit of an Alpha drive. Would this be a problem? Are the weight, size, and power requirements of what I'm describing such that the Bravo 3 is almost "mandatory" for satisfactory performance?
If anyone has any of the aforementioned boats or one similar I'd love to hear what drive package you have and how you like it.

Thanks,

Ayuh,.... With loads like that, a Bravo III is pretty much Necessary,.....

I'd say the 350 Mag is Minimum, a BBC would be a Better choice,...
 

Dave-R

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Mar 18, 2008
Messages
441
I think a 300hp. 5.7 in either the Mercruiser or Volvo will be plenty of power. I have both, one in a 226 Cobalt, and one in a Reinell 240c. I am at high altitude,but they will run close to 50mph. They are EFI engines though, I think the new carb engines are rated slightly lower. I am surprised that your engine is only 210hp. Is it a Vortec? A few years back we had a 21' Chaparral with 7.4 MPI Duo prop. It would fly onto plane and run to about 55 mph. It did use more fuel of course. I would not get the 5.0 if it were me. When you get the boat loaded, the last thing you want is for it to struggle to get on plane. I also would not shy away if one had the big block. The gas mileage will not be that different. Dave-R
 

KD4UPL

Senior Chief Petty Officer
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Feb 13, 2010
Messages
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Thanks for the responses so far. I should have mentioned I don't really care about top speed. We generally cruise around at about minimum planning speed. Towing the tube or something we might get to 35MPH or so. If I'm by myself I might wind it out but that's rare. I would certainly love to have a big block be it a 7.4 or an 8.1 but I'm not specifically looking for one because their even more rare than the 300 HP mag. My concern is mainly with getting on plane and towing a skier or whatever with all the weight on board.
Streffpilot, are you saying torque is irrelevant? Maybe I'm just used to trucks but I've always thought that for getting a heavy load moving and accelerating quickly lots of torque at a relatively low RPM is more important than high RPM horsepower. Wouldn't it be true to say that given a 5.0 and a 5.7 of the same HP the 5.7 would have greater torque due to it's longer stroke?
 

keith2k455

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Jul 23, 2012
Messages
558
I agree with your assumption...generally speaking, cubes = torque. We aren't talking boosted engines, so even though you may be able to find a 4.3 and 5.7 around the same hp (depending on yr and configuration), the 5.7 will have waaaay more torque.
 

QC

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Mar 22, 2005
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22,783
The reason no-one really talks torque is that (torque x rpm = HP). You can have all the torque in the world (for instance, an electric motor can even make gobs of torque at 0 rpm) but without the rpm, you won't be going anywhere. The torque at rpm is what makes HP, therefore, HP is what you need to measure for your application.
I love this guy!

Agree with Bondo, B3 solves the low end grunt issues and 300 HP will run low 40s pretty easily. The 260 5.0 is stronger than a 5.7 250. Especially with a B3. That's a big load you're talking about for sure. Even with a B3 I'd want a low pitch propset if that load was typical.

Edit: or Duoprop. Volvo has a 320 5.7 that runs as strong as a Merc 6.2 320. Good stuff both ways BTW.

Edit 2: to be clear, B3 or Duoprop gives a small block, single prop drive big block, low end performance. First hand experience.
 
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rallyart

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A dual prop drive is superior for many reasons. You could look at the new forward dual prop Volvo drive also. Price is the only reason to look at a single prop.
Horsepower lets you accelerate and gives you top speed possibilities. It takes the same fuel to run a 600 hp engine as a 200 hp engine in the same boat if you are cruising from planing speed to 35 mph. No cost savings from too little power when in use but there is, again, the price reason to get a less powerful engine. From an 'enjoy your boat' perspective, I have never heard anyone complain about too much power and I've heard many complain that they wish they had more.

In a fully loaded 23' boat you are going to need 'more' power if you are doing any water sports. The most enjoyment will be with a dual prop and max power engine. If that's too expensive, drop some power to save cost and drop some prop pitch. If that's still too expensive look at a little smaller boat, but keep the dual prop.

Enjoy. You are looking at nice stuff.
 
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dockwrecker

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You'd be suprised what just adding tabs would do to your existing boat. If what you're really doing is low speed tubing with a boat full of peeps, improving planing is the first priority. Smart tabs at least, helm hydraulics better. No reason to buy a new boat over this issue. (unless it's really an excuse for a new boat...)
 

Mischief Managed

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Dec 6, 2005
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I think a fuel injected 5.7 and a dual prop drive would be fine in that boat.

As others stated, trim tabs would make a huge difference in performance, regardless of the choice in power.

Torque is never mentioned in boat engine specs because it can be multiplied. Boat makers simply install a drive and prop that matches the engine to the boat. If your engine makes 360 ft-lbs of torque and operates through a 1.8:1 drive, the prop sees 648 ft-lbs of torque. If your engine makes 324 ft-lbs of torque and operates through a 2:1 drive, the prop sees 648 ft-lbs of torque. The difference is that the bigger engine/1.8: drive package spreads the torque over a broader speed range so it will accelerate a little better and have a higher top speed, assuming both engines weigh the same.


Longer stroke does not necessarily mean more torque. Torque is a function of displacement, thermal efficiency and volumetric efficiency. Increase any one of those parameters while the others stay the same and torque goes up. If those parameters remain exactly the same but the stroke increases, the torque peak will be at a lower RPM but the torque peak numbers will be the same (and the HP will be lower). Since HP is a function of torque and RPM, an engine that makes equal torque at a higher RPM will make more HP. That's why race engines rev so much. Unfortunately, for boats, making an engine rev high requires cam timing that can allow for reversion at low RPM and that draws water backwards up the exhaust passages and that's bad for the engine. The solution is to make the cam timing variable and that's why Volvo Penta is able to get 380 HP out of 6 liters while Mercruiser needs 8.2 liters to do the same.
 

KD4UPL

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Mischeif, thanks for the excellent lesson on torque.

Looking for used boats with everything you want at an affordable price narrows the selection. I'd thought about dropping the dual prop as a requirement to broaden the list of possible boats but it sounds like i need to keep it. I'm glad to hear the 260HP 5.0 is a strong engine, I see lots of these boat equipped with it. I will pass and take the 300 HP magnum as the minimum. I'd take a big block for sure but that narrows my options on boats even further. I'm not trying to save fuel, just purchase price. Most of my friends "get it" and chip in generously for fuel.

Dockwrecker, I hadn't thought much about tabs, I thought they were mostly for handling, loading, and balance issues which I don't feel need much improvement. I may give them a try this year if the current boat doesn't sell for me. I did go to a 4 blade prop a year or 2 back. I can't tell much difference but it didn't hurt either.
 

doyall

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May 9, 2012
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Ayuh,.... With loads like that, a Bravo III is pretty much Necessary,.....

I'd say the 350 Mag is Minimum, a BBC would be a Better choice,...

Agreed, but I doubt that any of these boats will be rated for a BBC.

I have a smaller boat to those the OP looks at (Azure AZ220 sportdeck, 4,400# dry) with the VP 5.0 rated at 270 HP with DuoProp and can't imagine a bigger boat with less power/torque.
 

H20Rat

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Mar 8, 2009
Messages
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Dockwrecker, I hadn't thought much about tabs, I thought they were mostly for handling, loading, and balance issues which I don't feel need much improvement. I may give them a try this year if the current boat doesn't sell for me. I did go to a 4 blade prop a year or 2 back. I can't tell much difference but it didn't hurt either.

Tabs let you get and stay on plane much easier. For water sports, especially tubing, it can drop your fuel bill and power requirements fairly drastically. Instead of the engine constantly having to fight the hull, the tabs let the hull stay up on top.
 

shrew

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Dec 29, 2006
Messages
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12 people on these boats?:

Larson 206Sei
Searay 220 Sundeck
Chapparal 233 Sunesta

I am very surprised that these boats can handle 12 people. It certainly won't be very comfortable. This is not really in the design range for the engine and drive package and I would expect most boats of this size range to perform poorly with this king of load. Where can you even store 12 PFD's on these boats?
 

KD4UPL

Senior Chief Petty Officer
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Feb 13, 2010
Messages
653
My current boat, the Larson is only rated for 11. That's part of why I want a bigger boat. My parent, brother, sister, and families make 12. It's really annoying to be 1 short of the right amount.
The Sea Ray and the Chaparral are rated for 12. It's only one more but it allows me to take the whole family. I think the Four Winns 234 I looked at was rated for 13 people. Since I regularly run my boat with 8 to 11 people a bigger one with more power should do fine with 12. If I count correctly I've got 12 PFD's on my current boat but it does take up just about all the storage.
The reason for the upgrade are really quite numerous. My boat is 18 years old and the floor is getting soft. The upholstery needs re-done. The wife wants a head and fuel injection (she's never really figured out starting a carburated engine). I want a fiberglass floor instead of carpet over plywood that I'm constantly trying to dry out. And we could certainly use more room since we like to bring lots of family and friends along.
I think if I can swing it the Sundeck 240 is the only one that might come with a big block and it's rated for 13 people. That would be my favorite option but, of course, also the most expensive.
 

Scott Danforth

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I have a boat rated for 12, however its crowded with 8. I would sell your current boat to one of the family members and get the next boat wish at a minimum a dual prop drive. I would recommend a stroked small block.
 
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