Outboard size for a 4.75 tinny ???

[scottar]

Re: Outboard size for a 4.75 tinny ???

I think the boat and type of fishing you do is important. For example, my hull is rated to 115 but I installed a Suzi 90 4 str.

Partly because the next size up went to a bigger block and the price leapt considerably. At the time I couldn't justify the additional dollars for the extra HP.

But it's only on glass out or in a river that I push it to WOT otherwise, in the bay where I go most, the hull is often only comfortable at 3/4 throttle (~4500 rpm).

So what I'm saying is that whilst the hull will handle more HP I'd rarely be able to use it due to the limitations of the hull. Instead I enjoy the better fuel economy all the time and just occasionally wish I had more. Plus the dollars I saved make the first few years worth of fuel free!

By the way, it'll top out at ~55km/h which is usually fast enough for me and hole shot is fantastic.

This does raise a point of interest with the "always fit maximum horsepower" train of thought. In principle, I agree but you need to ensure that by going to maximum horsepower in your chosen brand of power plant that you will not be introducing handling traits that will be annoying for most of the boats usage simply to gain that bit extra zing that will only be used on those all too rare occasions when conditions allow. I have seen this first hand with my own boat where the difference in engine weight produced a rig that has needed a considerable amount of tweaking to get it to perform as I wanted it when things weren't so nice (seems to be most of the time these days) . If the extra horsepower comes without weight penalty - not an issue as a general rule (it may use a bit more fuel though) but if the maximum horsepower brings about significant weight penalties, the grass is not always greener.

[NAGG]

Re: Outboard size for a 4.75 tinny ???

This does raise a point of interest with the "always fit maximum horsepower" train of thought. In principle, I agree but you need to ensure that by going to maximum horsepower in your chosen brand of power plant that you will not be introducing handling traits that will be annoying for most of the boats usage simply to gain that bit extra zing that will only be used on those all too rare occasions when conditions allow. I have seen this first hand with my own boat where the difference in engine weight produced a rig that has needed a considerable amount of tweaking to get it to perform as I wanted it when things weren't so nice (seems to be most of the time these days) . If the extra horsepower comes without weight penalty - not an issue as a general rule (it may use a bit more fuel though) but if the maximum horsepower brings about significant weight penalties, the grass is not always greener.

& that is a fair point ........ take my scenario the F70 comes in at 119kgs (996CC) . If you step up to the F80 (1596CC) - you add 49kgs & gain a modest 14%ish more power ....... but the F100 comes in with the same additional 49kgs but gains around 43% more power . so if you were looking at Yamaha .... you would either stay down at the 70 ( working it harder) or you go the 100hp .

Sometimes though you might find that another motor brand may be the best option ........ eg a Suzuki 90 comes in at 15kgs less than the F80 yammi but gains in power .

Chris

[fishwpa]

Re: Outboard size for a 4.75 tinny ???

This does raise a point of interest with the "always fit maximum horsepower" train of thought. In principle, I agree but you need to ensure that by going to maximum horsepower in your chosen brand of power plant that you will not be introducing handling traits that will be annoying for most of the boats usage simply to gain that bit extra zing that will only be used on those all too rare occasions when conditions allow. I have seen this first hand with my own boat where the difference in engine weight produced a rig that has needed a considerable amount of tweaking to get it to perform as I wanted it when things weren't so nice (seems to be most of the time these days) . If the extra horsepower comes without weight penalty - not an issue as a general rule (it may use a bit more fuel though) but if the maximum horsepower brings about significant weight penalties, the grass is not always greener.

Got me thinking about going the Suz DF175 on my BC 670c over the Min 150 & Max 200. Hoping the 175 will be the right choice - power to weight. I had a surtees 4.85 cc with a merc 4s 60hp on the back, max was 70hp I think and the Yam 70 from what I can remember researching has basically the same output as Merc 60 (not 100% on that). The Merc had no where near enough ponies out of the hole with 2 blokes on board it was dangerous but was basically the largest HP there was keeping it within weight limit. Wondering whether the 200 is the way to go.

[up the creek]

Re: Outboard size for a 4.75 tinny ???

if a suzuki 175 cant do it.. can a 200?? im sure a 175hp will be plenty on that size boat but like scottar said whats more important the weight or extra hp

[Moonlighter]

Re: Outboard size for a 4.75 tinny ???

175 and 200 4cyl Suzuki weigh the same. Easy choice, go the 200!

[gofishin]

Outboard size for a 4.75 tinny ???

It's funny how that, 'today', if an offshore boat doesn't do 40kn (or near to it), it is considered by many to be underpowered - yet our fathers, and possibly their fathers too, used to repeatedly and safely fish the same areas we fish... in boats with less HP, which were much slower and many with less reliable and less user-friendly 2 stroke O/B motors than our O/B's of today - regardless of their stroke cycle.

What's more, there was no such thing as a GPS or a Plotter. The 'all natural' coastal bars had no groins or nice big rock walls, and were a lot more treacherous. Sounders worked on paper or displayed depths by small flashing lights on a circular dial (anyone remember these??).

AND... there was no internet, live weather, wave and swell feeds, and the weather man's predictions were far from the 'highly accurate' (????!!) predictions we get today!

How did they/we survive all those trips??... and ... did our mothers really let us go out with dad 'in those slow dangerous boats' in those situations???

Ok, semi-rant ... with a touch of sarcasm ... is over [emoji1].

Yes, like many, my boat does 40kn. But do we really need it??? NO, don't think so!

This does raise a point of interest with the "always fit maximum horsepower" train of thought. In principle, I agree but you need to ensure that by going to maximum horsepower in your chosen brand of power plant that you will not be introducing handling traits that will be annoying for most of the boats usage simply to gain that bit extra zing that will only be used on those all too rare occasions when conditions allow....

Some wise words in your post Scotty, and I particularly like this ^^^ bit.

Other than considering any weight penalty very seriously, there is also another factor that I believe is very important, and always like to consider very seriously. This is... the 'consequence' of too much power (and hence prop pitch), and the resulting extra speed at the 'all too critical' lower engine revs/lower planing speeds.

To explain, we need to delve in to a bit of math and physics... easy to do... but who really wants to do/read/get their head around this stuff on a Sunday night??? [emoji1]

... but if the maximum horsepower brings about significant weight penalties, the grass is not always greener.

Yep, agree 100% Scotty. I would even say it is "rarely greener" [emoji1].
Cheers
Brendon