Replacing MD6B with Beta 16

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Stu66

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Hi everyone,

I’m looking into replacing the old MD6B on my golden shamrock 30 (displacement approx 3500kg). Non saildrive, fixed 3 blade prop (I think it may be the original LH). Prop walk is to starboard.

Does anyone know the exact measurement for engine mount bolt hole locations, and if Beta have matching ready-made mounts, or if custom will be needed? Also would any difference between old/new engine height, be adjustable just with the mounts, or would the bed have to be raised?

Is prop shaft angle 7 degrees?

Will a new shaft and prop be required?

Thanks
 
Beta will make mounts to suit your installation, well worth the extra cost as I would have had to replace the mounting bearers. For a Beta 25 in a Moody33, Check with Beta but I had to have a new prop and exhaust system as on opposite side. Beta are very helpful. I think for you would be better off with a 20 or 25hp. I was limited as the original engine was 35hp BUT I would have had to re-align the complete prop shaft.
 
There's a drawing here showing (standard) engine mount positions, extent of mount adjustment, engine height etc. here - B16 HE DataSheet REV 05 1121

As mentioned above, Beta will provide custom-made feet to fit the engine to the bearers if the standard ones do not suit.

That data sheet linked above also gives the various gearbox options, one of the standard options has a 7 degree down angle. Lots of other literature and technical info available on their website

Give Beta a ring (or email). They are very helpful, and will be able to answer all your queries.

You will need a new prop in order to take advantage of the additional power of the engine over your current one, apart from any other considerations (e.g. direction of rotation, engine/gearbox combination output speed). Whether you need a new shaft will depend on various factors, but I guess most probably you will.

As mentioned, you will likely need a new exhaust hose, etc.
 
The installation drawings are all available on their website. A 16hp is woefully underpowered for 3500kgs - 20 is the minimum to achieve hull speed. As said you will need a new prop and probably lots of other things as well. You can get a down angle gearbox as an extra (at extra cost) and only worth doing if your current beds are made for a down angle box and are difficult to modify or you have vertical clearance issues at the front. Otherwise better to modify the beds or have brackets made to take a straight box. The key dimension to work from is the prop shaft flange which is a fixed point, although you may be able to move it aft if there is enough room. You then work forward from this to find out how best to mount the engine. If you are going for a 16 to get the best out of it you may have to use a 2.6:1 reduction and probably a 15" prop, but you may then hit a tip clearance problem with the prop. With a 20 you have the power to use a faster spinning smaller prop.

I am just going through this process also with a Beta, but a 30hp. I have done 2 re-engine projects in the past so have some experience of the process. Be aware that the "extras" and professional fitting are likely to add at least 50% to the cost of the engine as not only will much of the old bits of the current installation be incompatible, but other things will turn out to be so worn that they need replacing.
 
You will need a bigger new prop. This will have more drag. Do yourself a favour and get a folder rather than a fixed blade.
 
Stu66 said:
I’m looking into replacing the old MD6B on my golden shamrock 30 (displacement approx 3500kg). Non saildrive, fixed 3 blade prop (I think it may be the original LH). Prop walk is to starboard.

Does anyone know the exact measurement for engine mount bolt hole locations, and if Beta have matching ready-made mounts, or if custom will be needed? Also would any difference between old/new engine height, be adjustable just with the mounts, or would the bed have to be raised?

Is prop shaft angle 7 degrees?
Click to expand...

Not exactly the same swap, but I have replaced a MD7A with a Beta 722 (20hp) in a 29" boat with a displacement of 3.6 tons.
The width of the engine footprint was almost the same, but the beds needed to be raised 45 - 50mm, from memory. The sump pan goes deeper than on the Volvo, but I think there is a shallow sump version available if space is limited.
My problem was a perceived lack of engine room length and in discussion with Beta they suggested the B16 (recently introduced at that time) for my boat.
But I had set my mind on a 3 cylinder engine and in the end it turned out to fit in the space available.
In retrospect I think the B16 would have been sufficient for my boat with regards to power, the spare capacity I now have is rarely used, if ever.

Edit: my installation is straight, non-angled.
 
Minchsailor said:
On my Nic. 32 I replaced the MD7A with a 13/14 (?) 2 cylinder Beta and it was fine. Think it was a 2:1 TMC 40 gearbox. Obviously a new prop, but they hardly break the bank.

Pushed it along adequately.
Click to expand...
While that sort of hp will move the boat - you only need around 10hp to achieve between 4.5 and 5knots in flat water, Your maximum is around 5.5 knots, whereas your potential maximum is 6.7 knots for which you need roughly double the hp you currently have.

My GH 31 has much the same characteristics as your boat but a bit less displacement and will be fitted with a Beta 30 which will allow cruising at less than half power (5.5 knots at 2400rpm) with plenty in reserve. Will use no more fuel than, say a 20 which would have to run at 3000rpm to achieve the same cruising speed. Fuel used is a direct function of power required, not the output potential of the engine.

Which approach you take depends almost entirely on your definition is of "adequately". You can of course overpower a displacement boat but because there is little penalty with a modern diesel in terms of fuel consumption or size/weight (for the OP 9kgs and 60mm length for a 3cylinder 20 over a 2 cylinder 16) it seems sensible to aim for the optimum of achieving hull speed at close to maximum rpm which gives cruising speed at half power.

Having endured many years of an underpowered boat (space considerations mainly) I know which I prefer.
 
Stu66 said:
Hi everyone,

I’m looking into replacing the old MD6B on my golden shamrock 30 (displacement approx 3500kg). Non saildrive, fixed 3 blade prop (I think it may be the original LH). Prop walk is to starboard.

Does anyone know the exact measurement for engine mount bolt hole locations, and if Beta have matching ready-made mounts, or if custom will be needed? Also would any difference between old/new engine height, be adjustable just with the mounts, or would the bed have to be raised?

Is prop shaft angle 7 degrees?

Will a new shaft and prop be required?

Thanks
Click to expand...


You can rely on the dimensions supplied by Beta but with an old engine I would always measure the existing engine, in order to get the size from the top of the bearers to the centre of the output shaft. It involves a lot of fencing with straight edges etc. You don't need to be terribly accurate but remember the standard feet will raise the new engine height by a nominal 65mm. This is adjustable of course but keep at the back of your mind the fact that if you end up with the output shaft a little low it is easily fixed with packing etc. Too high could be a catastrophe.
There are loads of useful things on the Beta site, esp look at a download of the Operator's Manual

Rather than special feet you may feel it is easier to use plates fixed to the existing bearers, which you can then drill to suit at your leisure. This is a useful plan if the new engine is narrower than the old, which may well be the case here.

You would need a new prop, I would use a new shaft as well unless the existing is perfect. You would need to think about other stuff as well but if the budget is tight new patent stuffing boxes, fancy couplings etc start to add up. 16hp would be fine on your boat though you might just think about the 20hp unit which is 3 cylinder. Any bigger and you would be spending more to drag a big prop around for no good purpose.

.
 
I see that the existing prop is left handed so it will need replaced. The Beta 30 that replaced my VP 2003 uses a right hand prop. That added an unexpected £400 to the cost for 2 RH Sillette folder blades. Anyone want 2 LH Sillette folder blades?
 
A Beta 20 is a 3 cylinder engine which is noticeably smoother than the 2 cyl variant and also comes with the poly vee belt which is a worthwhile thing just for belt dust!

A PRM 150 gearbox is availible for these engines at extra cost, these can turn in both directions so if you want to retain the prop swinging LH this is the way to go. There's multiple ratios if you post your current prop size I can comment of theres something that would work.

Posting a photo of your current engine beds would increase the quality of advice given! I find it's generally long term better to adjust the beds to the new engines standardvwhere its possible to do so, otherwise you end up with something none standard which makes things harder down the line.
 
I find that my 1978 MD7A (13.5 hp at the flywheel) has plenty of power to drive my 30.5 ft waterline/4 ton displacement yacht. I usually cruise at 6.5 knots/1650 rpm or so (redline is 2600 rpm). I could probably run it a bit faster and it really wouldn't mind. I have no plans to replace it, but if it eventually gives up I guess I'll end up with 16 hp because that's what's available now. I wouldn't mind replacing it with the same power either though.

I think a lot of people who seem to want over 7 hp per ton displacement probably have a completely inappropriate propeller on their current engine, or something like that. The old rule of thumb was 4 hp/ton, these days it's more like 5 hp/ton.

Tranona said:
My GH 31 has much the same characteristics as your boat but a bit less displacement and will be fitted with a Beta 30 which will allow cruising at less than half power (5.5 knots at 2400rpm) with plenty in reserve. Will use no more fuel than, say a 20 which would have to run at 3000rpm to achieve the same cruising speed. Fuel used is a direct function of power required, not the output potential of the engine.
Click to expand...

This isn't strictly true. It varies a bit from engine to engine, but most mechanically regulated and injected diesels have a specific fuel consumption curve that's vaguely U-shaped. That is to say, fuel consumption per kWh output is lowest somewhere in the middle of the rpm range but higher at very low and very high rpm's. The effect isn't huge, typically 10-15% or so maybe, but it's not insignificant either. Annoyingly Beta doesn't have these curves in their datasheets so you have to go dig them out for the Kubota base engine if you want to know.
 
If you You turn the same prop at the same speed you will absorb the same HP seems rather strange to spend £K? just to end up where you started
PROPELLERS DRIVE BOATS!
 
kblomster said:
This isn't strictly true. It varies a bit from engine to engine, but most mechanically regulated and injected diesels have a specific fuel consumption curve that's vaguely U-shaped. That is to say, fuel consumption per kWh output is lowest somewhere in the middle of the rpm range but higher at very low and very high rpm's. The effect isn't huge, typically 10-15% or so maybe, but it's not insignificant either. Annoyingly Beta doesn't have these curves in their datasheets so you have to go dig them out for the Kubota base engine if you want to know.
Click to expand...

In reality the variation in specific consumption makes very little difference to average fuel consumption - particularly when you re talking about the range of 1-2l per hour. I kept records of the consumption - that is volume used over engine hours on a 30hp 2030, mainly cruising at half power and pretty consistent at just under 2lh. My last boat was fitted with a 20 as standard and a 30 as option - most buyers chose the 30. For the same cruising speed the 20 would need 2500rpm against 2200 for the 30 - and the fuel consumption would be the same.

The rule of thumb ls just that, simply a number derived by dividing the displacement by the hp and has no theoretical basis. As scottie says it is propellers that drive boats, not engines. So you start with the ideal propeller size to achieve the target speed and then work out the shaft speed and power required to drive the boat. For many yachts the constraint is that you cannot fit a prop that is big enough diameter or arrive at a slow enough shaft speed to turn the large diameter prop.

If the objective is theoretical hull speed then you need, sing your crude method nearer the 7hp per ton than 3. On my GH when we did the calculations the ideal prop size was 17" diameter and power required to achieve hull speed was 26.5hp. The original engine was a 20hp with a 15" prop which would achieve 6 knots compared with hull speed of 6.8knots. My choice was between a Beta 25 or 30, both with a 2.6:1 reduction. A 25 would not achieve hull speed but a 30 would just exceed it, and give 5.5 knots cruising at 2400rpm.

As I said earlier, which way you go depends on your expectations and now using modern engines and efficient props (like the Featherstream I am fitting) allow much improved motoring performance over a wider range of conditions with greater refinement for little penalty in terms of cost or weight. Of course if you are happy with sub optimal performance under power then stick to a smaller engine.
 
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