Is driving a planing boat at displacement speed a false economy?

[Deleted User YDKXO]

We've just completed a nice 300nm meander through the Dalmatian islands in Croatia moving our boat from it's winter base in N Italy to it's summer base near Split. For the first time, I forced myself to do a substantial part of this trip at minimum in gear speed which on my boat happens to be 7.3kts, in order to save fuel. My smugness at having saved several hundred Euros worth of diesel soon evaporated however when I filled in the log book at the end of the trip and found that the trip had put about 30hrs on the engines, which is not far off half my normal annual usage. I then began to wonder whether the few hundred Euros I'd saved was more than wiped out by the extra depreciation I'd incurred by putting those extra hours on the engines.
So I started to think about the numbers on this. Say that 2 people, Buyer A and Buyer B, buy 2 new 45ft flybridge cruisers which they intend to keep for 5yrs. Buyer A doesn't care about fuel consumption and he cruises everywhere at 21kts consuming fuel at a rate of 20 gals/hr. Buyer B is a skinflint and closet ecowarrior and cruises everywhere at 7kts consuming fuel at 2 gals/hr. Lets assume also that diesel costs £5/gal and both Buyer A and Buyer B cruise on average 2100nm per season (equivalent to an average 100hrs at 21kts). Without going into the detailed maths but anyone can work it out, Buyer A will spend £10,000 per year on fuel and Buyer B will spend £3,000 per year which, after 5yrs, will result in a very handy £35,000 saving for Buyer B.
But here is the big but, after 5yrs Buyer A will be selling a boat with 500hrs on it and Buyer B will be selling a boat with a massive 1500hrs on it. Buyer B may have saved £35,000 in fuel costs over 5yrs but I bet that saving will be more than wiped out by the extra depreciation he has incurred on the value of his boat. Now you can argue about the reality of the figures and maybe you can argue that Buyer B is going to do less mileage in a season than Buyer A anyway. Maybe the logical conclusion of this is that if you intend to do displacement cruising, buy a displacement boat and them when you sell it, its not going to have more hours than other boats on the market. Maybe used boat buyers should be educated not just to judge a boat on engine hours but on total mileage covered, like cars. Or maybe the logical conclusion is that all we planing boat owners should blat everywhere at max speed to minimise engine hours
There's been a lot said on this forum and in the mobo mags recently about slowing down to save fuel but maybe we planing boat owners aren't really saving money at all by doing this?

 

[Whitelighter]

Dunno.

But on a side note, we are on a boat out if Trogir for a week in August - 40ft rag and stick thing so not massive range. Don't suppose you are about then?

 

[Deleted User YDKXO]

Dunno.

But on a side note, we are on a boat out if Trogir for a week in August - 40ft rag and stick thing so not massive range. Don't suppose you are about then?

Yup we intend to be on our boat from 9th to 30th August and it would be great to meet up. Trogir is about 20nm south east of where we are based

 

[oGaryo]

Mike, I think the question is summarised in not so much whether a saving is made either way but is the differential between the two that great that it warrants consideration. If no, then clearly, using the boat for what it's designed for is the way to go, planing. If the boat owner cannot afford that, then it's time to consider purchasing a true displacement boat where I presume it's expected that it'll have the high hours for the reason you've stated but they known it's not been thrashed so it'll hold its price

 

[Chris_d]

I've often wondered about this as being river based you tend to clock up loads of hours. When I first had twin engines I used alternate engines between locks to effectively halve the hours logged, but it was all too much hassle with odd steering and only one engine charging the domestics or heating the water etc... so gave up and just run them both now. Just have to resign myself to educating buyers when the time comes

 

[Vitesse]

According to Yamaha, a similar size / weight boat with the same outboard as mine is most efficient once it's planing. Around 3.5 mpg. There is a smaller peak in mpg / gph at hull speed.

SWMBO's favourite throttle setting when passing through Salcombe is just about the worst economy it'll give! Stern dug in and lots of wake...

No help at all to the OP, mind!

 

[jfm]

Yup, I think you have got a good point here Deleted User. The numbers will vary from case to case but your numbers are not bad imho, and the guy with the 1500hour boat has more than wiped out his £35k fuel saving imho

Just goes to show, whichever way you cut it, boats cost money, erk

I think the hours-to-value thing is not linear. I sold my last boat with 260 hours but the guy who bought it wouldn't have cared if 360. He would have cared if 650 becuase he is then facing the "big 1000" in his ownership. But I'm not arguing here with your basic premise - I agree it

1000 hours is of course nothing in engineering terms but it matters from a market point of view, like it or not.

The answer therefore has gotta be something like 1/3 pootling and 2/3 blatting at 21kts. Your numbers sort of say that pootling in small doses saves you instant fuel money, but don't over do it

 

[Divemaster1]

I'd rather have a well used engine with high hours than a low hour, poorly preserved one....

Frequent use and low load usually means better reliability in the long run... so a thousand (or a couple) hours on a decent & well maintained diesel engine over a 5 year period is not excesive... too many engines stand to death these days and once started up, people expect the animal to behave just like their car which they use every day... as in out of the drive and accellerate up, without thinking that this iron lump need more time to heat up, get proper lube around into high load components etc... then they go for a30 min blast and stop engine... leaving it to cool down and stay in a beautifully corrosive environment because shaft seals are dripping.... when they then lift the lid up a couple of months later, they wonder where the rust and seized components fome from ..... and end up blaming it on poor engine....

IMHO ... Give me a well used, and cared for engine any time !!

 

[volvopaul]

The hours wouldn't worry me as long as its been serviced every year wether its done the hours or not.

What I would be happy with is the saving on purchase price on the boat with more hours as it would be a good knocking point, though the fuel saving would help sell the boat as the overall asking price should be lower. All of course IMHO .

 

[volvopaul]

I'd rather have a well used engine with high hours than a low hour, poorly preserved one....

Frequent use and low load usually means better reliability in the long run... so a thousand (or a couple) hours on a decent & well maintained diesel engine over a 5 year period is not excesive... too many engines stand to death these days and once started up, people expect the animal to behave just like their car which they use every day... as in out of the drive and accellerate up, without thinking that this iron lump need more time to heat up, get proper lube around into high load components etc... then they go for a30 min blast and stop engine... leaving it to cool down and stay in a beautifully corrosive environment because shaft seals are dripping.... when they then lift the lid up a couple of months later, they wonder where the rust and seized components fome from ..... and end up blaming it on poor engine....

IMHO ... Give me a well used, and cared for engine any time !!

Quite right, I've seen so many 63p engines of late hardly used with heat exchangers that are nearly ready for the scrap bin, all because there left stood furring up, the same said boats gearshift lever on the g box was also seized solid!!! I heard it hadn't left its berth for two years apart from lifts out.

 

[Nick_H]

Interesting maths Mike. Maybe the answer is to blat about everywhere at 25 knots for the first 5-10 years, which will often cover first and second owner, then for later owners to slow down once the boat has suffered most of its depreciation. This probably suits newer owners who are unlikely to care much about fuel costs, and later owners who will often be more cost conscious.

Personally, if I was going to go everywhere at displacement speed i'd buy a sailing yacht and save nearly all the fuel cost.

 

[kashurst]

+1
however going anywhere on a sailing boat just takes forever, displacing at 8 - 10 kns and you feel like you are getting somewhere.

 

[Deleted User YDKXO]

Interesting maths Mike. Maybe the answer is to blat about everywhere at 25 knots for the first 5-10 years, which will often cover first and second owner, then for later owners to slow down once the boat has suffered most of its depreciation. This probably suits newer owners who are unlikely to care much about fuel costs, and later owners who will often be more cost conscious.

Yup I was thinking that. Maybe the canny way to go is to buy a low hours used boat (notwithstanding what the forum cognoscenti say about low hours) and then pootle about for a few seasons until the hours reach the market average?

 

[gjgm]

Yup I was thinking that. Maybe the canny way to go is to buy a low hours used boat (notwithstanding what the forum cognoscenti say about low hours) and then pootle about for a few seasons until the hours reach the market average?

But then why bother....take up golf or something.
I think the issue is a bit simpler to resolve...own a boat you can afford-whatever that means to you-to run.You do seem to be seeing more new boats with slightly smaller engines being popular...I guess not many owners need all that power to blat about all day,anymore

 

[burgundyben]

For me the fuel saving opportunity was going from thirty knots to twenty. We tried it and liked it. Fuel consumption prety much halved.

 

[henryf]

Strange that you should post this Mike. I was thinking exactly the same only the other day as we pottered over to the Hamble from Newtown Creek.

The other thing I pondered was just how the engines felt running at tick over for such a long period of time. Common wisdom seems to dictate that oil burners like to be put under a bit of load to avoid glazed bores.

I totally agree with Ben in that running 22 knots rather than 32 knots is possibly a more sensible saving. Also keeping tabs on how clean the hull and mechanical gear is.

If you fancy the odd potter to either extend range on a long leg or compliment your mood then fill your boots, but to set 7 knots as your norm might not work long term.

Henry

 

[Deleted User YDKXO]

But then why bother....take up golf or something.
I think the issue is a bit simpler to resolve...own a boat you can afford-whatever that means to you-to run.You do seem to be seeing more new boats with slightly smaller engines being popular...I guess not many owners need all that power to blat about all day,anymore

Yeah but there are plenty of owners like me who still want the option of either going fast or slow when the mood or the necessity take them and therefore a planing boat makes sense in terms of boat choice. At this stage in my boating life I neither want a D boat that is incapable of breaking 10kts and nor do I want a SD boat which uses even more fuel than a P boat at speed

 

[henryf]

Yeah but there are plenty of owners like me who still want the option of either going fast or slow when the mood or the necessity take them and therefore a planing boat makes sense in terms of boat choice. At this stage in my boating life I neither want a D boat that is incapable of breaking 10kts and nor do I want a SD boat which uses even more fuel than a P boat at speed

As you may recall we pondered some more left field choices before buying the P50 and I also concluded that planing boats still offered the best of both worlds. Especially as they get bigger and smooth out the water. Go even larger and stabilisers narrow down the displacement / planing hull design differences further still.

I have found a number of times being able to stay on the plane in less than perfect conditions keeps us from being thrown around. Slow to displacement speed and suddenly the waves exert greater influence on our comfort and stability. It's all about options.

Henry

 

[Deleted User YDKXO]

Strange that you should post this Mike. I was thinking exactly the same only the other day as we pottered over to the Hamble from Newtown Creek.

The other thing I pondered was just how the engines felt running at tick over for such a long period of time. Common wisdom seems to dictate that oil burners like to be put under a bit of load to avoid glazed bores.

I totally agree with Ben in that running 22 knots rather than 32 knots is possibly a more sensible saving. Also keeping tabs on how clean the hull and mechanical gear is.

If you fancy the odd potter to either extend range on a long leg or compliment your mood then fill your boots, but to set 7 knots as your norm might not work long term.

Henry

Agreed henryf. Nobody is going to buy a planing boat and do 7kts in it all the time but they might do say 50/50 between 7 and 20kts thinking they're making a big saving when in fact they're not. Actually with my boat, the fuel consumption only rises slightly between 20 and 30kts but I tend to cruise at 20-22kts because thats where I and the boat feel most relaxed. The longest trip we did at 7kts lasted about 8hrs and I found that pretty tedious. At that speed, there is an awful temptation to nudge the throttles forward a bit to do say 10kts but actually I found there was a huge increase in fuel consumption from 11 l/hr at 7.3kts to 30 l/hr at 10kts so, if you're going to do displacement cruising to save fuel it makes sense to go as slow as you can. At displacement speed, I also found myself very irritated by small noises and vibrations coming from the boat; on one particular day at sea, I took half the patio door apart trying to find a rattle
I will still be doing a few hours at slow speed this season but knowing that the actual cost saving may not be large, I think most of my season will be spent at 20-22kts again

 

[Vitesse]

Are you chaps measuring consumption with a fuel flow meter?