massive yet lightweight transom-ripping tender outboard info required

tcm

...
Joined
11 Jan 2002
Messages
23,958
Location
Caribbean at the moment
Visit site
mrs tcm has kindly organised a new RIB, 10.5 feet long and aluminium base which only weighs about 55kilos all in, in bright orange, special order from AB. It's rated at 25horsepower, so obviously it'll be good for loads more. Although it does say "don't put too much horsepower" on the info, but that's likely becos Budget Marine is a slightly american site. It doesn't say "yes, we mean it esp and specifically tcm", for example.

Son#2 suggested an airline engine but that's a bit ridiculous, and would melt the rubber, so being relatively more sensible, i reckon that 30 or praps 40 would be about okay in a sort of ooer aarg sort of way.

So does anyone know what is the very lightest new 30horsepower motor I can buy? It needs to be shortshaft, WITH an extension handle otherwise it might tip single person out over the back. Although you can sort of shuffle up/down the boat as it gets on the plane. Or 40hp, if it has better power to weight ratio, or maybe 50 hp bearing mind i stuck 15on the back of a dinghy rated at 8 and it was fine, but that's the absolute limiit really. I quite like two strokes cos they scream properly, like a real outboard should, whereas a 30hp 4-stroke is gonna feel like a weak car engine and nowhere near loud enough, and much heavier in a motorbike-grand-prix-losing way. I think 50kilos outright weight is quoted maximum. But there again, if a fat american got in, the 50kilos would be irrelvant, so treat the 50kilos as a guide, ish. It's gotta have just string start, no lectrics.
 
Re: massive yet lightweight transom-ripping tender outboard info requi

I don't think you're going to get a new 4 stroke 30-50hp motor that is anything like 50kg. Most of them are between 70-110kgs.

Even the E-Tec 2 stroke 40 weighs over 100kgs
 
Me thinks you ought to reconsider if this dink is for on your catamaran, unless you've got somewhere very sturdy to keep it as well a a decent way to lift it. But then again, I seem to recall that you had a big cat with lots of toys, so maybe you do have somewhere suitable to keep it.

An engine of that size is going to be f'in heavy and a complete PITA to get on and off. If the engine plus dink are going to hang off davits you'll need some chunky ones to be able to withstand a bit of bouncing around in a seaway.

I saw a Farr 60/65 over the summer with a davit that had gone capput cos he had an Avon rib with a 50hp bouncing around on the back. Didn't do his boat much good when he hauled the broken davit back on board, which then proceeded to gouge his teak and gelcoat.

Also, I was nearly a contenter for the Darwin Awards when trying to get a 47kg 15hp Honda four stroke off the back of my rib whilst on my own. Needless to say, I've now got a sensible 26kg (?) 9.8 2stroke that will plane with a few peeps in the dinghy, provided they're not all family sized pie eaters. That's on a 9ft fibregalss RIB - an ally one is prob much lighter, so even better.
 
davits etc

yep the davits are quite fab, andf fine even if the rib got lots of water in it. To lift engine on/off dink i use long line from mast lectric winch via boom block. curent yamaha 15hp is 36kilos and rib empty bout er 88kilos (zodiac 310 rib) means i shoulod be able to get 40hp total (rib plus motor)with same weight as 15?
 
Re: davits etc

What you need, if you can find one, is a Mercury/Mariner 30hp light version, which weighs under 50 kgs. It's 2 stroke, so not easy to find. Alternative is Tohatsu 30 hp 2 stroke, at similar weight. Lightest 40 hp is Tohatsu 2 stroke, at under 60 kgs from memory.

If you have to go 4 stroke, then lightest 30hp is Honda at 68 kgs, and 40hp is Yamaha at very heavy kgs. Lots of 20 hp's are under 50 kgs, but that's a bit off the pace.

Extension handles are cheap and available everywhere
 
Flipping Coliholic

Erstwhile poster hereabouts Coliholic could probably eat quite a large family as a morning snack, and got flipped out of of 3.6m dinghy with inboard 175hp so-called jet rib whilst aiming to crack 50knots.
 
This

500Yamato.jpg
 
Re: davits etc

I've got a 40hp Yam on the back of a 3.4m Walker Bay which is only rated at 30hp.
I only went for the 40 because it's obvious from the technical data the the 30 and 40 are the same engine with a few adjustments.
The boat is around 100kgs and the engine is about 90kgs from memory.
It works just fine although the dealer insisted on fitting these before handing it over.
IMG_5009Medium.jpg


If you start off slow, the bow rides a worringly high - solution is give is a quick blast and she literally "jumps" onto the plane.

Another solution is when two are aboard - put one in the bow.

I only really went for the bigger engine so that there's enough grunt when we get round to towing toys.

Your case isnt the same as ours - the RIB is lighter in the first place. I'd say go for a 30 but 40 would be still be OK - IMO
 
Re: davits etc

Mercury do a 2 cylinder 30hp (429cc version) that weighs about 50kg, they also do another 2 cylinder version (644cc) thats about 75kg for the 30hp but the 40hp on the same block weighs less than the 30hp.

Yamaha only do 2 cylinder blocks upto 25hp (49kg) and a 3 cylinder 30hp at 60kg. The 40hp blocks are over 75kg.

I reckon Nick S has it right with the 30hp Mercury/Mariner small block version. (With extra nitrous and stainless straight through exhausts for the essential TCM touch /forums/images/graemlins/wink.gif)
 
Yup, Nick h is right. Normal 4 strokes will be 70kg+, hoda being lightest. But if you can get a merc small block 2 stroke you have what you're asking for. Not sold in some countries, but prob avaialbe where you are. Hurry, before Brunswick goes bust of course

Merc have a fab lightweight uber reliable battery-less EFI. The first pull of the start string doesn't start the engine. It charges a tiny battery/capacitor. This then powers the EFI computer so on the second pull of the string the engine fires with EFI working. brilliant

I've just ordered the 2009 version of Hurricanre's engine, Yamaha, which is same as Hurric's but has EFI instead of 3-carbs and a new casing. It's 80kg so doesn't fit your spec and needs battery, and has hydraulic trim etc

Also when tuning it to make a nice noise, remeber on a 2s outboard much of the nice noise comes from the air intake rather than the exhaust (which is always muffled cos underwater). Loverly harmonics as the reeds open and close. So if you remove all the induction sound boxes and have a straight thru inlet you'll get a lovely noise
 
I think its time for some experimentation. Could you fill your new tender with helium,say, and give feedback on the handling charecteristics. This might enable you to get some real meat on the transom?
 
Well one wouldn't. Twud be kettle calling pot black. I have however ordered a set of 30 decals for my Yam 40 so it will be fine. I might have to borrow your dremel for the maker's plate - I assume you have a stencil to engrave a 4 into a 3?
 
You might be in for a surprise when you try this rib. I have driven one with a Yam 15 Hp 2/stroke on it and it felt like plenty. and I mean plenty! The alley hull is quite narrow and the ride is high and flighty, didn't fill me with confidence I'm afraid.

Hurricane's Walker Bay340 on the other hand I thought would be well over cooked and it wasn't. The layout of the seats were exactly right and if anything we had to move people to the rear to get the trim right, with a passenger forward, it rode bow down. Due to weight, I would recommend the WB310 it still lightweight but can have a console and far better tender (capacity) Far more stable and turns flat like it's on rails, similar to a ZapCat. /forums/images/graemlins/cool.gif

I can't be sure that we're talking of the same alloy rib here but it sounds the same spec. I would strongly recommend you try one first, even if it's with a smaller engine, you'll see what I mean. If you can get to the south coast I'm sure we could arrange something as there's one in Sparkes next to me.

Just be careful, the limits are there for a reason!
 
Top