"Saddle" fuel tanks ?

[Boo2]

30 hours is only 80 or so litres. Pretty small tank. I have 150l which gives me well over 300nm at cruising speed.

Hi Tranona,

I don't know what engine you've got ? Sunrunner had a Thornycroft 90 (38 hp 1500 cc) and is being re-engined with a Nani N4.38, it's modern (almost) exact equivalent.

The old engine gave 1 gallon per hour at cruising revs and the spec sheet for the Nani unsurprisingly gives about the same at cruising revs, rising to 2.5 gph at max power.

Sailing down to Shoreham from Pwllheli last time fuel was always an issue and I intend to do the crinkley bits of this great island this summer where refuelling is not going to be as easy as it is on the South Coast.

I'm changing the complete propulsion system (apart from the prop), engine, p-bracket, shaft, fuel tank, lines, the lot. I'd be a complete numpty if I didn't try to deal with this issue at the time when access is best.

Boo2

 

[Boo2]

why not carry extra fuel cans, or is that too simple

With respect, and please don't think this a criticism, but you do seem enthusiastic to the point of ( unnecessarily perhaps? ) determining to make things more complicated and set yourself huge amounts of work, expense and possible aggro. For questionnable benefit..
I perfectly understand if the forum posting is part of the evolving thinking process-like single line reefing- rather than This-Is-What-Im -Gonna-Do,--Because..
KISS for a year or two maybe? Just buy 5x10l diesel jerry cans and fill from syphon tube is my suggestion.
30h is over a day of solid motoring without refill. Ireland or France innit without refilling at sea.

Multi tanks/breathers/fillers/ links/airleaks/cleaning/space occupied,.. ugh!
I would rather get one decent quartertank built to maximise a dead space

Last boat I went in had 2 fuel tanks (under berths) connected to main tank in the bilges, like OP wants (it was lower, they just drained into it) supplying the engine. One of those tanks has been a water tank before, but as the need for fuel is important...
And then we carried jerrycans and a barrel of some 80 l. Theoretically we could use the fuel from the tanks and replenish them.
Theoretically.
I can assure you - when fuel is a matter of safety, like entering harbour in stormy condition, you must be certain it will be there until berth is reached, not that you will be hurriedly dancing with jerrycans on 20 foot breaking coastal seas, trying to get fuel into your tank instead of that water sloshing on decks.

Somehow in my boat fills are not on decks...

For the reasons Rossynant gives I don't want to use jerry cans for fuel storage. I do have one 5 gal jerrycan on the boat but that is hard enough to store and I much prefer to install permanent tankage.

My question here really was intended to find out the technical details of how supplementary tanks need to be installed, rather than looking for alternatives. Of course, if fitting extra tanks was too expensive, or a worse compromise, then I will use jerry cans but I don't want to consider that as a starting point.

Thanks to everyone here who has posted about possible issues and recommendations regarding things like valves, lines and vents,

Boo2

 

[Tranona]

Hi Tranona,

I don't know what engine you've got ? Sunrunner had a Thornycroft 90 (38 hp 1500 cc) and is being re-engined with a Nani N4.38, it's modern (almost) exact equivalent.

The old engine gave 1 gallon per hour at cruising revs and the spec sheet for the Nani unsurprisingly gives about the same at cruising revs, rising to 2.5 gph at max power.

Sailing down to Shoreham from Pwllheli last time fuel was always an issue and I intend to do the crinkley bits of this great island this summer where refuelling is not going to be as easy as it is on the South Coast.

I'm changing the complete propulsion system (apart from the prop), engine, p-bracket, shaft, fuel tank, lines, the lot. I'd be a complete numpty if I didn't try to deal with this issue at the time when access is best.

Boo2

Think you will find in practice that you will use somewhere around 3l per hour when cruising. My engine is 30hp Volvo and uses just over 2l hour. These sorts of figures are very commonly quoted on the many threads on here on the subject. So your 80l will give you well over 20 hours. Your tank is relatively small because the boat was not designed for long distance cruising. If you look at modern cruising boats of similar size you will find tanks of between 100 and 150 litres - mine has 150.

So you could do with more capacity and the obvious way is to install a bigger tank, but appreciate with the hull shape you have space is limited. The next best alternative is a completely separate second tank with changeover valves. Of course you may find it difficult to fit one for the same reason your current tank is small. The simple alternative is 2*20 litre cans which will increase your range by 50% but you will need to find a way of transferring fuel safely. This is what I had for my trip across the Med which gave me a range of over 400nm at cruising revs, although my longest leg was only 300 and I only transferred fuel once as a precaution because my gauge is dodgy, despite fitting a new sender.

 

[William_H]

Additional Fuel taank

I think if it were me I would be fitting the tank you wish with a separate filler and an electric pump to transfer to the main tank. A fuel gauge for the main tank would be very useful.
I did just this on a car I had once and it was very successful. I got another 50 litres to pump into main tank when main tank got low.It was convenient to tap the pump outlet into the main filler and I also teed off the vent for main tank. The vent was via a vapour recovery system. (yes petrol)
I like the way I could easily mange fuel capacity and needs via the normal fuel gage. You might ask why extra range. We were in to touring in outback Oz and 900km between gas stations is common. (4WD Mitsubishi van) gone now olewill

 

[macd]

you must be certain it will be there until berth is reached, not that you will be hurriedly dancing with jerrycans on 20 foot breaking coastal seas, trying to get fuel into your tank instead of that water sloshing on decks.

If there's 20-foot breaking seas, perhaps one should be sailing rather than motoring...in the opposite direction

 

[Rossynant]

But we were from opposite direction. After 10 days we wanted to the pubs!
After all you have a boat to get someplace. If she cannot take you where you want - what's the use?

 

[macd]

Suit yourself. I like piva as much as the next man, but 20 foot breaking seas (as opposed to seas with a bit of foam at the crests) approaching harbour are enough to roll most yachts. People die in such conditions.

 

[sailorman]

So what there is no mention of ocean cruising. I sized my fuel storage on my last boat on a lack of wind on a Biscay crossing, something I have experienced more than once. The OP has some 30 hours fuel storage and would like more, a desire I have sympathy with. My point was quite simply that in some boats using cans to top up at sea can be problematic which may be why fitting additional internal tankage had an attraction, it may just be the potential simplicity of all internal tankage and you then introduce the idea that it is all to do with ocean passages. I rally don't see where this applies to my comments and why you apparently attacked me over this, and still try to defend your attack.

Not an "attack" on anybody.
the OP stated
[Quote:
Originally Posted by sailorman View Post
what endurance do you have now & are you hoping to do extended ocean sailing
30 hours, yes (eventually anyway).
Boo2 ]

I then stated that the UFO 34 was originally a Cruiser / Racer & did he have the correct boat for his "hoped for "trip

 

[prv]

Not an "attack" on anybody.
[...]
I then stated that the UFO 34 was originally a Cruiser / Racer & did he have the correct boat for his "hoped for "trip

The confusion arises because you made your general point that a UFO 34 is not an ocean cruiser, but you posted it as a specific reply to Maxi77's point about juggling jerrycans in a seaway. There's no obvious link or relevance between the two, so why the quote?

Pete

 

[maxi77]

Not an "attack" on anybody.
the OP stated
[Quote:
Originally Posted by sailorman View Post
what endurance do you have now & are you hoping to do extended ocean sailing
30 hours, yes (eventually anyway).
Boo2 ]

I then stated that the UFO 34 was originally a Cruiser / Racer & did he have the correct boat for his "hoped for "trip

But why did you try twice to suggest I was saying any thing about ocean trips, and you are still at it. I really do not see why you seem intent on having a go at me.