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Old 09 September 2018, 18:02   #1
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GRP Boat OB Question

I find that this forum is best for any technical question related to boating hence posting my query here. Could we have a thread for "other boats' please? The immense knowledge here is not limited to RIBs/SIBs I believe.

Anyway, after a short stint with a SIB, I have narrowed down on a Corsiva 595 Tender as my next boat and am planning to order a new one for the next season. The aft is 5.7m and beam is 2.2m with the boat weighing around 600 kilos.

What OB would you recommend for the usual river pottering on the Thames and occasional cruise through tidal Thames. I am looking for something which provides a smoother boating experience with reasonable maintenance costs.

The dealer recommended OB is a Mariner 15hp which I am not too sure about. Thought of going private for the OB and spoke to a separate dealer who apparently turned out to be the OB provider for the boat dealer and tried best to talk me into just buying what the boat dealer is recommending. I agreed with him and just explored his thoughts on the hp to which he said there is not much difference between the Mariner 15hp and 20hp and that with a 25hp I will probably just get the advantage of a lower rpm, albeit minimal.

Being a complete OB illiterate, thought I would seek some opinion here. So, key questions are:

1. Is a 15hp sufficient for a boat this size?
2. Is Mariner a good option?
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Old 09 September 2018, 20:03   #2
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Wow.. that's a bit of a step up! There must be all manner of used boats that would do the job of that one at a quarter of the budget... and already have a few light scuffs so you wouldn't have to be so precious with them.

However if you want new then so be it.... nothing wrong in that.

Re outboard. I see on their spec sheet they will supply it with the same Mariner 9.9 as I've just bought for our SIB. I really can't imagine that little OB powering such a craft at almost 19ft long, weighing over 1000lbs for hull alone & with a capacity of 6 folks. Frankly I think it would feel a bit weak with a 15hp too.

If you want to go on the tidal Thames is there a speed limit where you want to operate and if not had you hoped to plane? If so you'll need to ask the makers/suppliers advice on min OB size for that performance laden. Perhaps 40-60hp??

If you are keeping to displacement speeds I still wouldn't under-outboard... you will still need some grunt and a decent prop size to operate it laden with confidence in locks and around other boats etc.

Just on gut feeling at minimum I'd be considering something like a Honda 20hp with a 4-blade prop upgrade.
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Old 10 September 2018, 02:59   #3
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Is it supposed to plane? I haven’t spotted a picture of the hull profile but my guess is it is for pottering around in rather than zipping about - although confusingly it is described as “fast”. Presumably the dealer (and the OB dealer) both know the boat and what you intend to do with it - why do you assume they are wrong?
Have you been on one afloat? (And what engine did it have, how did it perform, how many people were with you?)
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Old 10 September 2018, 03:10   #4
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At displacement mode the max speed of this boat is somewhere between 6&7 kn
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Old 10 September 2018, 04:25   #5
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it states max 60hp most river boats i see are in the 20hp range i would go for something like a yamaha 20 hp high thrust i had a 60hp on a fast fisher 500 great engine designed for heavy boats and displacement speed
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Old 10 September 2018, 04:40   #6
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What does come to mind MysticPuzzle is in your "hello" initial post you had been planning to get a cruiser. Given the budget you are considering now might it be worth making the step to something with a bit more shelter, cooker, toilet etc?
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Old 10 September 2018, 05:22   #7
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If you’re taking it on the tidal Thames you need more power. The river can be brutal when in full flow especially around the bridges & the Pool of London. You would be going backwards or sideways
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Old 10 September 2018, 09:08   #8
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Thanks for all the input, guys.

So far I have managed to get on couple of these boats but all had either 25 or a 30hp. Only one guy went for the higher power but others just used what they had on their previous boat. The boats handled really well and dealing with locks much better given the overall stability and control compared to a SIB. I couldn't find a boat with a 15hp which I could try so far hence the confusion. These boats plane, at least going by some videos on Youtube but with a 40hp or a 60hp. The dealers are probably correct in advising a 15hp considering that these boats are largely used for lazying around on the Thames and visiting the various Boat festivals and Regattas but what my concern is whether even for this purpose, are 15hps just about enough or I can do with a higher power which will give a better/smoother cruise. Planing is not on my agenda due to speed restrictions and I don't think I will be thinking about the sea for at least another 4-5 years.

Pikey Dave's comment about Tidal Thames is valuable and I may have to ask the dealer to advise appropriately. I was intending to go for a 25hp but will seek further opinion.

Fenlander, as for the boat choice, you are correct- I was always keen on getting a Cruiser with added benefit of a cabin, toilet etc. I wanted something in the range of 20 feet (to not spend a lot on mooring fees) and had narrowed down on Shetland 4+2 and a Viking 20 but had to change my mind as soon as I stepped into one of them. The problem- my claustrophobia Plus the social space on these cruisers around the helm is limited and shallow which could be a problem for our son.

A friend of mine who owns an Antaris Fifty5 recommended the Sloop and it fit in every bill. It is an open space with helm at the stern meaning I can keep an eye on the kid, reasonably deep to not worry about our son falling overboard accidentally, enough seating for just my family and dog or if we wanted to invite a few friends over; converts to a really spacious double bed to easily accommodate all 3 of us in case we ever feel adventurous and plan to moor overnight somewhere; comes with cruising canopy to deal with the elements and has steps to get out and in at Locks, lots of storage plus easy access to all areas of the boat. The Sloops do have a dry toilet but with pubs and restaurants littered across the Thames in our area, I don't think we will ever use it. Another option was a Bowrider but the Sloop faired better comparatively.

Buying a new Sloop was never my intention but used ones are rare and even if one becomes available, it sells in just a couple of hours for the asking price despite registering a very high interest with the Marinas. My interests are still in the used ones for all the reasons you mentioned in your initial reply but the dealers have a deadline to order new ones for next season which saves EUR3000 on transport/delivery. Guess that's business.

I still covet the cruiser and may buy a bigger one once the little one is a bit older.

If you have recommendations for another boat, please do tell.
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Old 10 September 2018, 15:16   #9
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OK well...

The Corsiva 595 is a very specific design based on the type of tender you might see in the med ferrying rich folks from posh motor yacht to harbourside eatery and piloted by a guy in ironed polo top/shorts with a radio clipped to his belt. A lot of its near 20ft length is taken up with the housing that is intended to hide the fact it's OB powered, the flash "captains" position and the bow seating arrangement. For that length I'd like a more flexible layout.

So I feel from my experience of river use on parents boats this may not have the ideal combination of attributes for a family day out craft.

Also I've found the river can be a place where you're far more likely to suffer wear and tear damage in locks and around other craft, scaffold pole/plank mooring stages, muddy river banks etc. So for me and as you are still new to all this I'd think of something smart but not mint where the odd little error would not make you tear your hair out with that first scratch.

So I'll pitch this that sold last year at our local inland marina... and something I thought huge value under £5k. It's in your length requirement, nicely fitted out, a practical layout with a useful "down below" area and enough shelter for all folks on board during a summer shower.

That would totally meet you needs I reckon and your thoughts on what's right or wrong in your eyes (or if you hate it) might help narrow down you real requirements.

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