Engine dilemma

[victoraspey]

Last year we began importing the motorcat into UK (www.motorcat.com) and I am in a dilemma what engines to fit to the next demo boat. The boat is a fairly new idea and therefore continues to surprise. After some trials this week with smaller engines I found the comparisons very revealing:

2x75hp outboards give speeds of 27 knots
2x50hp outboards give speed of 22 knots
2x8hp outboards give speed of 10 knots
1x2hp electric engine on recent trials gave speed of 5 mph

Whilst the motorcat concept is basically an extremely efficient twin displacement hull reaching a top speed of 27-28 knots it seems to be even more efficient at lower speeds. I do not know the river and broads market very well. As the motorcat has low wash and is environmentally freindly should the boat have river/broads appeal with smaller engines as well as sea?? Is there much interest in electric power?? Any sensible comments would be appreciated in helping me to understand.

 

[hlb]

Hmm. When I look to buy a boat from an importer or dealer. I look to him for advice, but a bit obvious, if you fit the big engines you can show the effect at each speed and let the customer decide whether he wants to go 27 knots or five. Maybe to simple!!

 

[DepSol]

Personally I would go for the 2 x 50hp sort of middle of the road. depends what did yuor last one have ? Did it sell quick? what were the comments about it ie feedback.

If you have middle of the road engines then you can cover both grounds.

Dom

 

[victoraspey]

I feel confident giving advice for boats used at sea and most go for the 2x50. Some are being used on the river with 2x50 but seems a bit of a waste of power if max river speed is 6 mph and it could be acheived with 2x2hp. Generally 2 hp petrol outboards do not have electric start. Electric engines require large battery banks. I am not very familiar with the broads. I agree that a dealer shoulld give best advice and I am doing my research. I wondered what opinions I would get on the forum on this subject.

 

[AJW]

Realistically a totally River based user is going to want electric starting and more importantly battery charging. So twin 4 strokes (for slow running performance) with enough alternator output to charge your domestic battery bank reasonably well are going to be needed. Twin 2hp outboards with pull start and internal fuel tanks isn't going to work. I reckon that twin 8-25hp are going to be favourite with the larger engines for someone say who is on non-tidal Thames but wants to occasionally go on the tidal bit. I don't think the infrastructure exists for purely electric drive although this could be interesting for pure river/broads use.

Shame she is semi-d, otherwise you could see what she goes like with a couple of 200hp opti's strapped to the back end /forums/images/graemlins/wink.gif

 

[Chris_d]

I've boated on the Thames for over 30 years and saily boats on the sea. In my experience most river boaters are frustatred seagoers, just waiting for the day when they can head down the tideway and open the throttles. However in reality few ever make it, hence there are a very high proportion of massively overpowered motor cruisers based on the river (and probably the broads as well).
Purpose built river cruisers with small engines to suit are now very rare, people will prefer to buy a stylish high speed sports cruiser, with huge turbo diesels or V8 petrols than buy that trudgey old purpose built river cruiser, with all its blue blazer and Terry and June type conertations. It doesn't matter that its completely unsuitable and overpowered, it just says that they are a seagoer if they want to be and the boat is capable. Hence nobody will buy the small engines unless they are being completely rational and honest about their dreams, and since when was a boat a sensible purchase. So I'd fit the 2x50hp as a compromise with the promise of extra speed, if they specify the really rare hot 2x75hp (just for you sir as you look like you can handle the power) fast version. If you put 2x8hps on there they will probably buy a b$%£&y narrow boat instead.
Forget electric power its for dayboats only.

 

[victoraspey]

I wonder about 2 hp electric with a diesel generator. 16 batteries for say 8 hours between charging. If no charging point use the generator or is this defeating the object? A bit worried about the bearing of extra weight on speed as it is untried but must take into account that virtually no fuel required and of course no 2x50hp outboards.

2x25hp should still be good for coastal use.

 

[Andrew_Fanner]

Thinking Thames and following on from Chris_d's remarks about frustrated seagoers (yup, I kinda fit that profile). Assuming 2 x 9.9 4 strokes, how would that perform in a stiff stream or, and the boat is obviously capable, on the Tideway tripping to St Kats or Limehouse? Ditto twin 15s, boith engine sizes being common enough on smaller cruisers sold with river/canal performance in mind. While 10 knots from two 8hp engines sounds perfectly viable against 4 or 5 knots of grumpy Thames tide, is that caning the engines or a sensible cruise? If caning, I for one would be very insistent on a power reserve, for cruising I'd still want to know that a single engine would get me back to safety if I had ventured into the more interesting bits. So, how would she perform on 1 x 9.9, 15 or 25?

Scenarios that occur are the Thames based boater going to Central London or maybe fancying the Medway, the Severn based boater who wants to go down to Bristol or maybe Cardiff or the Fenlands/Great Ouse woner who wants to cross The Wash. Assuming proper planning/competence of course!

 

[victoraspey]

Twin 9.9s - Power curve I have estimates around 12 knots max but it has not been tried yet. Experience so far suggests this is correct. No problem with seaworthiness - it is class B

Twin 15s power curves suggests max 14 knots - but again not tried but experience suggest this is correct

10 knots from 2x8 hp engines would be flat out so it would be caning the engines against a strong 5 knot tide and strong wind to make much progress.

Performance on 1 x 9.9 curve suggests max 8 knots
Performance on 1x15 curve suggests max 10 knots
Performance on 1x25 curve suggests max 13 knots
Perfomance on 1x50 - I can confirm getting max 16 knots in line with power curve

Boat steers happily on 1 engine - hardly noticable except when mooring up is not so easy. Single engine more efficient than twins.

Dont see any problems for anyone going on the journeys you outline.

 

[Marsupial]

Hi

Looking at the options (If I were based in the thames or broads) I think that I would opt for twin 50's with two sets of props. Its probably ok to power the boat with 2 x 2hp engines but is this realistic? what happens when the wind gets up? - there is no substitue for the ability to put a lot of power into the water when you need it. BUT running large engines at low revs is certain to reduce their life, hence two sets of props. One set for the dream one for the reality.

Just a thought

Regards

David

 

[Andrew_Fanner]

Sounds like 2 x 25 could be a good compromise between economy, low stress on engines, charging capacity and the ability for fairly occasional trips onto tidal waters. If I were tidally based or a very regular user of tidal waters I'd go for the 50s.

Curiosity compels me to query the effect of 2 x diesel outboards. Weight might be an issue...

 

[CaptainThames]

Agree with 2 x 25 as a good river compromise with a little extra in that combination for occasional tidal waters. This would work well for demo purposes while the benefit of outboards surely being that the prospective owner has a vast choice available with 2 x 10 available for broads and total river use which would also knock the price down. Resale should not be too affected as new engines could be fitted and old ones sold on if the next owner wanted to operate at higher speed. I blame a lot of overpowered cruisers on rivers on poor advice form brokers, mailnly based on a lack of more suitable river cruisers to sell, based on few purpose built river cruisers in production. I have met a number of new boaters with 25 foot (+ ot - a few feet) sports cruisers with 200 - 300 HP having great difficulty getting the hang of the power when manoeuvring in locks etc. Most have said that brokers convince them that this boat on the sales pontoon is just what they need. I do agree however that a number wish to get to sea at some stage and therefore it makes sense to have a few extra HP down below rather than have to go out and buy a new boat. Back to the outboards, stick to 4 strokes as slow spped running and 2 strokes is not so good although oil injection has improved things. Also agree that electric is not yet an option until you can be sure of having power points in places that you weould wish to stay overnight. Those fitted on the Thames so far are generally adjacent to locks and often away from the nicer areas. Local councils need to be encouraged to add facilities to their morring spots etc etc etc. Best of luck, I believe there is a demend for sensibly powered river cruisers, not sure what they will make of the lowering bow section. Saw one in Bembridge over Easter, up on the beach just inside the harbour. It was attracting a fair bit of attention.

 

[victoraspey]

Thanks for that post - it is beginning to galvanise my thoughts a bit. Investigate 2x2 hp electric with the broads and river authorities for the ecologically friendly market, maybe even hire cruisers. Upper thames 2x9.9hp. Lower Thames 2x25hp. Probably use Honda 4 stroke. More power than this required for heavy coastal and speed merchants up to 2x75hp. Evinrude ETEC injection is best for 2x75hp due high power to weight ratio. I have no brand preference between 25-75 hp.

Diesel outboards are around but a little agricultural. The exception is Yanmar 27hp diesel used by the military but it is hideously expensive. Best hope lies with injection outboards like ETEC which are being run on diesel, petrol, aircraft fuel by the US military but not available to the public at the moment.(ie. engine can be reprogrammed for different fuels - multifuel)