370 vs. 435.

[serpa4]

I've seen 2015 and 2016 with both the 370hp and the 435 hp engines.
65hp sounds significant esp. if I want to cruise at 18-20kts for 6-8 hours to the Bahamas.
I have a feeling I should stick with 435 hp boats.

 

[Shano]

We have a 2017 with the 435, we also have long distances to go to get to the fishing grounds or cruising grounds, at least 23nm and up to 40 nm one way. So we cruise at 18 to 20 knots which is between 70 and 76% load. If we had a 370, I am assuming, because I have never been in CW30 with that engine, we would cruise at about 17.5% less nmh to stay at the same load factor. So for me, cruising at slower speeds is too boring and I don’t always have the time to cruise slower because we do a lot of day trips fishing where the round trip is between 46 and 80nm. I wish we lived closer to where we go but... Also our last two boats were faster so it is tough to go down in speed — kind of simlilar to trying good wine and spending a bit more and then trying to go back to the less tasty stuff! Good luck with your decision. More seriously tho, I think that to cruise at 18 to 20 knots would be pushing the 370 too hard. Maybe Brian will give you some advice on that.

 

[Automaticman865]

I gave this some thought back a while ago. The Cutwater28 comes with the D4-260 and they (Volvo) also have the D4-300. So I thought why not have the more powerful engine taking up the same space. This is the same as the D6-370 and the D6-435 have the same exact displacement. 5.5 liters and 336 inches. So If you look at this similarly like John deere does in its M ratings, yes you'll get more horsepower but at the expense of more wear and tear on the engine. As Tony Athens shows in his articles that 2 gallons per liter and under you'll get closer to M1 rating. I would rather have the smallest horsepower engine out of a group all using the same block (same liter displacement). so yeah you could go faster but at the expense of the enging longevity and the extra fuel. Dont believe me check out the specs on a John Deere block and look at the M ratings and the horsepower all from the same block. An M1 can go greater than 3000 hours uninterrupted in 1 year, an M5 is less then 300 hours in a year. You do the math and this ends up being roughly 35 hp per liter for uninterrupted longevity in the engine.
Stuart

 

[BB marine]

The best way to answer the Question. Is the D6 370 hp adequate to push the C30 at 20 knots for hours without exceeding the manufactures recommendation of continuous operation at no more than 90% of WOT rpm? Meaning 3500 rpm -10% = 3150 rpm. The additional HP doesn't always relate to a large increase in speed instead the added HP helps maintain speed when additional load is added or sea's get sloppy. It takes a lot of additional Hp to make a boat increase speed especially a semi-displacement boat.

The 435 Hp and the 370 HP are the same engine. Same block, add a some additional air and fuel and you have more HP.

The 370 hp average burn is approx 15 gph at 3150 rpm. The 370 hp at WOT burns 20.3 gph. Using fuel burn to calculate load the 370 hp running continuously at 75% load 277 hp at 3150 rpm if WOT is 3500rpm.

The 435 hp average burn is approx 17.5 gph at 3150 rpm if WOT is 3500 rpm. The 435 at WOT burns 21.4 gph. Using fuel burn to calculate load the 435 hp running continuously at 80% load 348 hp at 3150rpm if WOT is 3500rpm.

Based on Shano's Specs 435 hp 73% load is required to cruise 18KT to 20KT = 317 hp. The 370 hp would need to run at 17.4 gph to make 317 hp which is approx 85% load.

The 370 hp and 435hp are the same block, injectors, turbo, same engine with ECM programing making the hp increase. Both engines are 5 rated engines. Max hp at rated rpm 3500rpm +150 rpm - 100 rpm. 1h WOT for 12 hrs and continues operation no higher than 10% of Max engine rpm. Thats the catch regardless of engine model maximum continuous rpm is 3150 rpm if max rpm is 3500 or above. The load forces on the 435hp at 3150 rpm are greater than the load forces on the 370hp at 3150. The engines are rated at variable load applications. This means operation at between 85% to 20% with average overall 30% to 40% load factor. Or you can use the 2 gph per engine displacement liter calculation.What this means is the overall average fuel burn should be no higher than 11 gph for the 435hp or 370 hp while operating between 85% to 20% load. That should be very easy to achieve with the D6.

The big deciding factor would be $$$ If you can find a 435hp priced right best choice. If you find a 370 hp in pristine condition priced right and the sea trial proves that your conditions can be met 18 to 20 kts at 3150 rpm or lower I would not hesitate. Both engines are the same and I would not hesitate to push the 370 hp harder than the 435hp. The 370 at WOT is equivalent load as the 435 hp at 85% load. Unfortunately running the 370hp WOT is not recommended because of engine speed.

My fuel estimates are based on calculations. They may be slightly different in use based on load and propping.

 

[FWTMD]

Agreeing with all of the above, but the same point said a bit differently.

Remember, the rated horsepower is the max horsepower.

The actual horsepower at a given moment is a function of how hard you are pushing the fuel burn (RPM). Without looking up the actual specs to be more precise, at half the max RPM it will be operating at half the rated horsepower.

The higher rated horsepower gives more room overhead to push things harder and faster.

The impression forms you want to run things with the hammer down, always, or often. You may not be happy unless you have the biggest hammer available.

Its just a personal choice to make

 

[serpa4]

I would think the higher horsepower motor would last longer. to do 20 knots say it takes 300 horsepower doesn't matter if it's 300 horse of a 435 or 300 horse from the 370 horse engine. using 300 horsepower of a 435 but seemed to be less high strung than 300 horsepower of 370 available hence making the motor last longer.

https://www.volvopenta.com/brand/en-en/ ... 20908.html

if I'm not wrong it sounds like the 435 has a larger turbo, larger intercooler, intake, larger cooling system, and larger injectors.
But maybe that's not what that article is talking about in the link.

 

[ixlr8]

I would think the higher horsepower motor would last longer. to do 20 knots say it takes 300 horsepower doesn't matter if it's 300 horse of a 435 or 300 horse from the 370 horse engine. using 300 horsepower of a 435 but seemed to be less high strung than 300 horsepower of 370 available hence making the motor last longer.

That would be true IF the 435 HP engine had a larger displacement than the 370 HP engine. BUT in this case, both engines have the same displacement. Therefore if you use 300 HP from either engine, the wear will be the same.

 

[BB marine]

if I'm not wrong it sounds like the 435 has a larger turbo, larger intercooler, intake, larger cooling system, and larger injectors.
But maybe that's not what that article is talking about in the link.

You question/statement sparked my interest so I reviewed a parts manual for the D6 370 and D6 435. My previous statement "The 370 hp and 435hp are the same block, injectors, turbo, same engine with ECM programing making the hp increase" Is not completely factual. The block is interchangeable differences include, pistons, head, injectors, compressor ,turbo, after cooler, heat exchanger I assume but can not state these part changes are do to the increase in HP between the 370 hp and the 435 hp D6. My opinion is these parts changes have to do with increased air and fuel flow do to the increased hp. My opinion is still the same. If I was in the market for a C30 and I found a C30 powered by a 370 in pristine condition and sea trialed it and it met my performance criteria ( cruising at 20 Kts at or below 3150rpm) Priced competitively ( less than the C30 with the 435hp ) I would not hesitate to purchase it. Without running both a C30 and comparing the performance differences of the 370 and 435 it is all speculation and opinion.

My experience in this subject is in the C26. I had the opportunity to purchase a pristine 2012 C26 powered by a Yanmar 4BY 180 hp. The slightly smaller displacement compared to the D3 220 and the addition HP was the decision I choose to Purchase a C26 with a 220HP. My thought was I could cruise faster at a lower rpm with the additional HP. I never sea trialed to compare. I ruled out the 180 hp and spent 1000's more on the C26 with the 220 hp. Reality is there isn't that much difference in performance based on information I have received from owners of the C26 with 200 hp and 180 hp. The only place there is a noted performance difference of 1 to2 kts depending on load @ WOT. At 3200 to 3400 rpm the performance is very close. It takes a great deal of power to push a semi- displacement hull thru the water. My conclusion is If the owner of a C26 with a 180 Yanmar and a owner of a C26 with a D3 220 both cruise at 12kts. the longevity of the engines is going to be the same. The difference may be 100 or less rpm higher with the smaller engine. Decisions based on fact and reality are the best. Speculation and opinion have to many variables. You can also use the theory of "Go with the maximum Hp you will always have it but don't have to use it" That theory negates this thread there is no reason to ask!. Good luck with your search for the right boat.

 

[Godspeed]

I have a 2015 C30 with the smaller HP Volvo. As someone else stated it was in pristine condition when we bought it 2 years ago with only 60 hours and the 5 year Volvo warranty. I would have preferred the additional HP but it was not a deal killer.
We use the boat a lot. With 80% fuel load, no fresh water and no waste I achieve 17 knots at 3170 rpms. I can get up to 20 knots at 3250 rpms but don’t do this for over 5-10 min to catch a bridge. The fuel economy is likely the bigger difference at higher NMPH. At 17 knots I’m only getting about 1.5 NMPG. At 14 knots I get between 2-3 NMPH. I think the higher HP Volvo would get better NMPG at higher speeds. Most of our trips are across LK MI at 50-80 NM per leg. Just enjoy the journey. The extra 20 min on a 60 NM crossing is not that big a deal to me. I would estimate I also use 5-10 additional gallons of diesel compared to the higher output D6.

But again, it was the right boat at an exceptional
price so I have no regrets.

Find the best boat at the best price and then factor in the value over 5-10 years of the higher HP to your cruising style.

I hope this helps

B

 

[Shano]

I have a 2015 C30 with the smaller HP Volvo. As someone else stated it was in pristine condition when we bought it 2 years ago with only 60 hours and the 5 year Volvo warranty. I would have preferred the additional HP but it was not a deal killer.
We use the boat a lot. With 80% fuel load, no fresh water and no waste I achieve 17 knots at 3170 rpms. I can get up to 20 knots at 3250 rpms but don’t do this for over 5-10 min to catch a bridge. The fuel economy is likely the bigger difference at higher NMPH. At 17 knots I’m only getting about 1.5 NMPG. At 14 knots I get between 2-3 NMPH. I think the higher HP Volvo would get better NMPG at higher speeds. Most of our trips are across LK MI at 50-80 NM per leg. Just enjoy the journey. The extra 20 min on a 60 NM crossing is not that big a deal to me. I would estimate I also use 5-10 additional gallons of diesel compared to the higher output D6.

But again, it was the right boat at an exceptional
price so I have no regrets.

Find the best boat at the best price and then factor in the value over 5-10 years of the higher HP to your cruising style.

B

Your fuel efficiency numbers are impressive!
I should clarify some of my previous numbers - I use the Volvo %Load gauge as one of my main indicators. So when I wrote at 18 to 20 knots we are at 71 to 76% load I should have added that the rpms are between 2900 and 3000. Our wot is 3640. At 80% fuel and empty water and waste and neutral current we get about 1.30 nmpg at the 18 to 20 knot speed. At 14 knots it is about the same maybe a little better but nowhere near 2 nmpg. We have a 25 hp kicker on our boat so with the fuel tank, fuel, power assist pump, and cabling that is close to 300 pounds extra we are packing. Also, curiously, when we go from fresh to salt water the fuel efficiency goes down somewhat. At wot we get about 26 knots. I rarely go to wot other than just to see what the wot rpms are. Also, weight carried makes a big difference on our boat. When we are returning from a trip with lowish fuel, empty water and empty waste we can get up to 1.35 to 1.4 nmpg. So it seems from Godspeed’s actual numbers at 20 knots the 370 is at about 90% of rpms and from my numbers the 435 is at about 80% rpm (tho our boat is a little heavier than most CW30s). So for the original poster asking the question it appears both engines would get the job done within the manufacturer’s recommendations with a fuel efficiency edge going to the 370.

 

[BB marine]

I have a 2015 C30 with the smaller HP Volvo. As someone else stated it was in pristine condition when we bought it 2 years ago with only 60 hours and the 5 year Volvo warranty. I would have preferred the additional HP but it was not a deal killer.
We use the boat a lot. With 80% fuel load, no fresh water and no waste I achieve 17 knots at 3170 rpms. I can get up to 20 knots at 3250 rpms but don’t do this for over 5-10 min to catch a bridge. The fuel economy is likely the bigger difference at higher NMPH. At 17 knots I’m only getting about 1.5 NMPG. At 14 knots I get between 2-3 NMPH. I think the higher HP Volvo would get better NMPG at higher speeds. Most of our trips are across LK MI at 50-80 NM per leg. Just enjoy the journey. The extra 20 min on a 60 NM crossing is not that big a deal to me. I would estimate I also use 5-10 additional gallons of diesel compared to the higher output D6.

But again, it was the right boat at an exceptional
price so I have no regrets.

Find the best boat at the best price and then factor in the value over 5-10 years of the higher HP to your cruising style.

B

Your fuel efficiency numbers are impressive!
I should clarify some of my previous numbers - I use the Volvo %Load gauge as one of my main indicators. So when I wrote at 18 to 20 knots we are at 71 to 76% load I should have added that the rpms are between 2900 and 3000. Our wot is 3640. At 80% fuel and empty water and waste and neutral current we get about 1.30 nmpg at the 18 to 20 knot speed. At 14 knots it is about the same maybe a little better but nowhere near 2 nmpg. We have a 25 hp kicker on our boat so with the fuel tank, fuel, power assist pump, and cabling that is close to 300 pounds extra we are packing. Also, curiously, when we go from fresh to salt water the fuel efficiency goes down somewhat. At wot we get about 26 knots. I rarely go to wot other than just to see what the wot rpms are. Also, weight carried makes a big difference on our boat. When we are returning from a trip with lowish fuel, empty water and empty waste we can get up to 1.35 to 1.4 nmpg. So it seems from Godspeed’s actual numbers at 20 knots the 370 is at about 90% of rpms and from my numbers the 435 is at about 80% rpm (tho our boat is a little heavier than most CW30s). So for the original poster asking the question it appears both engines would get the job done within the manufacturer’s recommendations with a fuel efficiency edge going to the 370.

The increase in the fuel consumption in a semi displacement boat propped correctly with added load is noticeable by as much as 10%. Example: A boat that cruises light load burns 1.5 mpg. A loaded boat may increase fuel consumption to 1.35 mpg. 15gph may increase to 16.5 gph. This relates to more HP needed to push the boat. A boat powered with a 370 hp C30, needing 10% more hp = 37 hp to push the boat because of added load. (20hp=1gph) ( 10% = 37 hp= 1.85gph more). The 435 hp powered boat C30 with the same load would also need 37 hp to push it the same speed less than 10% hp but still 37 hp. It takes the same amount of fuel to make 37 hp.

Example: if it takes 300 hp to push a C30 18kts it doesn't matter if you have a 370 hp or a 435 hp it takes the same hp to push the boat. If maintaining 18KTS the RPM may be less with the 435hp by 100 or 200 RPM but the HP being developed is the same.

The semi-displacement hull gets good fuel economy when there is a bow wake. Hull speed or slightly above. My C26 gets average 4 mpg @ 6.5kts 1.9gph. As soon as the stern wake increases and the bow wake decreases 7.5 kts the fuel economy goes down 3 mpg 2.8gph as soon the bow wake is gone and stern wake increases the fuel economy averages 2 mpg ranging from 2.2 mpg to 1.70 mpg I would suspect this is the same for all the Cutwater models and Rangers (Semi displacement design). The larger R31 and C30 probably less than 1.70 at higher speeds.

A C30 @ 14kts achieving 2.3 mpg to 3.45 mpg is awesome. The best I ever got with my C26 220hp D3 @ 14kts is 1.80mpg

 

[serpa4]

I wonder if the propeller pitch and/or diameter is the same between the 370 and 435?

 

[BB marine]

There would have to be a change of prop (pitch/diameter) or gear ratio to maintain the proper WOT RPM. A 30' cutwater with a 370 hp will not be able to turn WOT recommended rpm with the same prop and reverse gear as a 30' Cutwater powered with a 435hp that turns 3600RPM. Most boat manufactures work with engine manufactures. The the 370 and 435 hp have different optional gear ratio selections. Changing the prop only to accommodate added hp is not always efficient. The manufactures will sea trial to find the best combination same ratio with prop changes or different ratio with same prop. In some cases different ratio and prop.

 

[serpa4]

Hopefully those who replied to this thread can chime in on my performance during a sea trial of a 2015 C30 with the larger 435hp.
Empty boat for equipment.
AC/Generator.
Clean, but painted bottom.
160 gallons of fuel.
about 1/2 water.
5 adults.
calms seas no current.
Sea level in Florida.
After the fact: Propeller is fine, no damage. Engine makes max RPM. No smoke. Normal engine temps.

Fuel stats:
1400 rpm 1.6gph 6.8kts
1800 rpm 4.3gph 8kts
1900 rpm 5.1 gph 8.2kts
2800 rpm 14 gph 14kts
3000 rpm 15.8 gph 16kts
3000 rpm 16.0gph 16kts
3450 rpm 22 gph 20kts
3500 rpm wot 22.1 gph 21 kts

So, if I "should" maintain 80% load based on fuel consumption that means about 16gph sustained, max sustained speed in this C30 is about 16kts. However, I'd still add more water and living supplies which would be slower.

So, somewhere between 14kts and 16kts should be fine for a long haul.
However, the extremely poor mpg kills my requirement to be able to go 250 miles at 17-20kts.
At 16kts and 16gph, this makes for a range of only (162 usable gallons / 16 gallon/hr = 10.12 hours @ 16kts = 162 nautical miles) or 186 statue miles with a 10% reserve.

I also went on a ride with a friend's 2020 C30/435hp
Boat had living stuff, cloths, food, cleaning supplies, spares, etc.
AC/Generator running while boating.
Unpainted bottom.
150 gallons of fuel.
Unknown water.
4 adults.
Warm day
In a fresh water lake (less dense / less boat buoyancy and boat sits lower in the water with more wetted surface area?) Maybe more prop slip due to less dense water (fresh vs. salt). Humans float better in saltwater.
800ft altitude.

14-15gph at 20.3 kts
At 20 kts and 14.5 gph, this makes for a range of (162 usable gallons / 14.5 gallon/hr = 11.17 hours @ 20.3 kts= 226 nautical miles) or 260 statue miles with a 10% reserve. This is a 75 statue mile mores than the 2015 at a 4 kts/20% faster! On a long jump, that is a couple hours difference.

Last week I turned down the purchase of the 2015 based on it's inability to make a couple of the Bahama island jumps without making a fuel stop on the longer jumps. A couple of the jumps between islands and no fuel stops is over 200 statue miles.
I'll keep searching for one with better mpg.

 

[BB marine]

That is interesting to see the difference in the 2020 and 2015 performance. Weight is a key component with a Cutwater inboard. It is not a planing hull. Your numbers on your friends boat do not show rpm's. What was the WOT rpm of the 2020? Fuel = hp Using your numbers 1 gallon of fuel produces 19.5 hp . At 14 kts it is using theoretical 275 hp to push the boat at that speed. Your friends boat is using (15 gph) 292 hp to push the boat at 20 kts. The numbers don't add up ( hp is hp) Something is wrong. Weight of the boat must be significantly different. Is the 2015 water logged ? Bottom dirty? It doesn't take much crud to slow a hull down. I would question the fuel flow reading from the gauge to real usage. The fuel flows are fairly accurate but a small picture of 5 minutes of run time is not always that accurate in true usage. I usually see a 10 to 15% difference in real usage. Example: yesterday we filled up. The Garmin and Volvo both agreed we burned 48 gallons of fuel. I filled the tank ( took 35 minutes to get the tank full) I wanted to make sure it was completely topped off ( I did this on the last fill up too) because I have a 225 mile run to do without filling up ( I'm not considering cruising over 7.5 knots) I was able to squeeze 41 gallons in the tank and made a mess doing that! This shows almost 15% error in actual fuel usage.

There must be a large variable between the 2020 D6 435hp and the 2015 D6 435hp in tuning?
There must be a different prop used with more efficiency ?
There must be a great deal of weight difference between the 2015 and 2020 C30

For some reason the comparison is not apples to apples. Maybe the Cutwater reps can chime in and give a list of differences that enhanced the performance of a new C30 over an old C30. Same Hp different performance.

Good luck with your boat search. I would suggest looking at a planing hull diesel powered boat. You will see better fuel economy and performance. Probably not going to find one that is trailerable though. The Back Cove 32 would be my choice.

 

[S@LTD]

One thing eluded to here is air flow. If you are at altitude it makes a huge difference. There is a guy on Lake Tahoe and the 370 would not plane up. Bring the boat to sea level as it was fine. This was early on and Volvo switched out to the 435 and he has been a happy camper ever since.