Bukh DV20 replacement

[europe172]

What are the best options for a replacement of a bukh dv 20?
I could go for an ex lifeboat engine but if I want a lighter and smoother running engine which can heat hot water which would be the best?

 

[LittleSister]

You don't need to change your engine in order to be able to heat hot water, the DV20 will do it just fine. I have a direct (seawater) cooled Bukh and it heats water well.

There is an article specifically about adding calorifier to a Bukh on the excellent website of Vyv Cox (of this parish). Calorifier installation

If you are going to change from a Bukh, though, you have a range of engines which are lighter in weight. Almost all of them, though, will likely require significant changes to propellor, exhaust system, fuel system, start/stop control panels and wiring, etc. etc. so don't ignore the potential significant cost of that in addition to the engine itself.

I was very satisfied with a Beta I had in a previous boat, and especially how helpful Beta were with advice, fast supply of spares, etc., even though I had not been the original purchaser of the engine. Some suppliers of similar but different brand engines have a rather less favourable reputation on that after-sales/parts supply front.

 

[Tranona]

What are the best options for a replacement of a bukh dv 20?
I could go for an ex lifeboat engine but if I want a lighter and smoother running engine which can heat hot water which would be the best?

Depends on the boat. Many boats fitted with the DV 20 were underpowered, but a Beta 25 will make the best replacement with a useful increase in power for boats up to around 4.5 -5 tons displacement. above that worth going up to 29 np. This assumes you want to be able to achieve hull speed. On the other hand if your boat is lighter performance cruiser a Beta 20 (or any other of the 20hp engines on the market) will probably do.

Much more to deciding the best re-engine package - boat, stern gear arrangements and particularly type of use and expected performance. Once you have the data the actual choice of engine is straightforward, but as Little Sister says the parts and process of fitting is more complex. I have just had a Beta 30 installed professionally and the breakdown of costs was was roughly 70% engine, 30% labour and installation components - although that did include complete replacement of stern gear but not the propeller. So when you look at engine prices work on 25-30% extra for installation.

 

[vyv_cox]

I replaced my Bukh DV20 with a Yanmar 3GM30F. A very easy change that has been well worthwhile. Apart from power, quietness and smoothness increases it weighs 90 kg less and left enough space above it to insert a very handy tool box.

 

[europe172]

I replaced my Bukh DV20 with a Yanmar 3GM30F. A very easy change that has been well worthwhile. Apart from power, quietness and smoothness increases it weighs 90 kg less and left enough space above it to insert a very handy tool box.

Thanks for that info, how was the engine bed spacing ?was the shaft rotation the same ?

 

[doug748]

What are the best options for a replacement of a bukh dv 20?
I could go for an ex lifeboat engine but if I want a lighter and smoother running engine which can heat hot water which would be the best?

Few people argue with Beta as a replacement esp if UK based.

It will also depend, to a certain extent, on the boat design; if your prop exits in a cavity behind the skeg or keel not only will you want to keep the prop dimensions down but may find cavitation and transmission noise does not deliver the quiet motoring you might expect. It does at least mean that you can hide a two bladed prop when sailing. For these sorts of considerations you need to have a good reason to increase engine size, unlike motor cars, boats don't always have the potential to go faster because you put in more horsepower.

.

 

[Kwik Decision]

I had the Bukh DV20 in our (previous) Sadler 29 replaced with a Beta 25 9 yrs ago. Excellent service / support from TS Marine, who are one of Beta's biggest agents. I was originally going to put a 20 in, which would have been sufficient power, but price (and size) increase to go from 20 to 25 was tiny. The new engine was smaller, lighter, smoother and quieter than the Bukh, and was 100% reliable in my ownership. I do know that the next owner had to replace the raw water pump (a Jabsco or Johnson pump) at around 6 yrs old due to a leak though.

 

[vyv_cox]

Thanks for that info, how was the engine bed spacing ?was the shaft rotation the same ?

We needed the engine to be raised 1 inch. Used steel bar drilled and tapped for mounting bolts but hardwood would have worked. Rotation was the same and I kept the same prop for a season. Exhaust and seawater inlet bigger.

 

[dankilb]

I do know that the next owner had to replace the raw water pump (a Jabsco or Johnson pump) at around 6 yrs old due to a leak though.

I hope they kept / rebuilt the old one as a spare?!

They leak after a while because the rubber lip seal has a mild steel spring inside that perishes. Ours went after about 8 years. A £10 replacement seal (available with stainless insides) and a bit of fettling to fit it saves about £300 (ours is a 50hp, so more expensive pump, mind).

Sorry for the thread drift!

 

[Tranona]

Thanks for that info, how was the engine bed spacing ?was the shaft rotation the same ?

The engine mount spacing for the Bukh is 390mm. The Yanmar 3YM is 370mm, as is the Beta 25. Beta 30 is 410mm. So you will have to build the beds in or out as appropriate. Different ways of doing this, but not normally a big issue. The height may well need adjusting, but this depends on the individual engine/gearbox combination as the drop from crankshaft to gearbox output varies. Most modern gearboxes give a RH propeller rotation as standard, but some give an option. However you will need a new propeller whichever new engine you choose. The Bukh revs to 3000rpm and the standard gearbox reduction is 2.5:1 giving a shaft speed of 1176rpm whereas many modern engines rev to 3600rpm and standard reduction is 2:1 giving a shaft speed of 1800rpm or 2.2:1 for the Yanmar, shaft speed 1636rpm - a substantial difference. There are of course alternative gearbox reduction ratio boxes available as options.

As I suggested earlier you need to forget what you have now and start from scratch with the basic data for the boat and any structural constraints (as doug 748 says prop clearance is often a major constraint), decide what level of performance you want to achieve and do the sums to arrive at the best combination of engine/gearbox/propeller.. The differences between the choices can be quite stark. With my project the hp required to achieve hull speed is approx 26, so a 25hp would almost do it (the original engine was a 20hp) and a 30hp would exceed. However the difference in top speed is well over 0.6 knot (6.3-6.9) and crucially for the smaller engine a comfortable 5.5 knots cruising requires 2600 rpm rather than 2200rpm. Although fuel consumption is the same (this is a function of power required, not RPM) the lower revs is much more comfortable and relaxing. Cost may of course influence your decision, but it is in fact minor in the whole cost of the project. The difference between 20-25hp and 25-30 is around £600 for each step for the engine but all other costs essentially stay the same.

Good luck with your deliberations.

 

[europe172]

Good luck with your deliberations.
[/QUOTE]
Thank you for that , really useful information and @vyv_cox thank you for the excellent web site information. I think if I can easily get hot water I will stick with the bukh as I got a folding prop last year and it would hurt to replace that

 

[Tranona]

You may not need to change the prop as it depends on what combination of engine/reduction ratio you chose and the extra power can often offset the increase in shaft rpm. That is why vyv's prop worked. The 10hp increase was enough to deal with spinning the prop sized for lower revs. Usually with folding props you can just change the blades if it is really well out!

However, I agree, if your main objective is just to get hot water you have just saved yourself £8-9k but will forgo the other benefits of a modern engine! Interestingly while my Beta was being installed the boat next to me (a Fulmar) was having his Bukh replaced with a reconditioned unit at I guess from what the owner said well under half the price of mine.