Too much outboard?

BoatyMacBoatface · 22 July 2020, 21:59

Evening guys

New to this and wondered if i could call on your knowledge please?

I currently have a new 20hp Mariner EFI 4 stroke outboard, and would like to get an inflatable that will compliment its performance... but must still be able to be thrown in the back of the 4x4.

I've been looking at the Honwaves and in particular the T32 IE Air deck. The problem I can see is that its only rated for a 15hp outboard, and i don't want to go to the expense of replacing it.

The 20hp Mariner is the same weight as the 15hp Mariner or 15hp Honda equivalent at 45kg.

If I put the 20hp on and never run it above 3/4 throttle then would this be OK, or are there other issues I'm not factoring in?

Also, if I did run this boat/outboard combination at full throttle is it likely to damage the SIB? Or is the 15hp max rating to keep the speed below 20mph for insurance purposes?

Thank you in advance.

smallribber · 23 July 2020, 05:04

A 20 hp 4 stroke will be too big and heavy for a T32. Have a look at the T38IE (far better boat) or one of the Excel crafts

Jung at Heart · 23 July 2020, 05:54

Here’s my T38 IE2 with 20hp Honda 4 stroke, fuel tank, life jackets etc. Packed in to back of my camper van, you’ll get this in to the back of your 4x4 I imagine.

My novice opinion is that 20hp on the T32 would be too much, the T38 is more suitable if you’re sticking with 20hp.

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BoatyMacBoatface · 23 July 2020, 06:13

Quote:

Originally Posted by smallribber

A 20 hp 4 stroke will be too big and heavy for a T32. Have a look at the T38IE (far better boat) or one of the Excel crafts

The T32 is rated for up to a 15hp Outboard?

But the 15hp Honda is the same weight as my 20hp Mariner. So i had it in my my head the weight wouldn't be so much of an issue, but the extra 5hp of power might?

I dont really need a 3.8m boat as it will only ever just be me in it. So was thinking a smaller boat, with more power to weight ratio = better performance.

I am a novice though so I might have that all wrong?

Jung at Heart · 23 July 2020, 07:27

Quote:

Originally Posted by BoatyMacBoatface

The T32 is rated for up to a 15hp Outboard?

I'm a novice here too, i imagine someone that knows their stuff will answer this for you comprehensively.

The only other contribution i can offer is that using a larger outboard than your boat is rated for could invalidate an insurance claim?

If you keep the engine is there another 3.2M SIB that has a higher outboard rating, that's how i read smallribber's suggestion if you didn't fancy the larger T38.

jeffstevens763@g · 23 July 2020, 07:51

this is a nice boat

https://www.excel-inflatables.co.uk/...volaire390.php

willk · 23 July 2020, 07:57

Quote:

Originally Posted by BoatyMacBoatface

I dont really need a 3.8m boat as it will only ever just be me in it. So was thinking a smaller boat, with more power to weight ratio = better performance.

I am a novice though so I might have that all wrong?

IMO, you have.

It may seem counterintuitive, but the 3.8m will likely go faster than the 3.2m with a 20hp. The extra few cm in length equates to very little extra weight and the longer hull provides superior planing qualities. If you can manage the extra cost and can move it around, the 3.8m with the 20hp is a no-brainer.

jwalker · 23 July 2020, 11:14

I'm with willk, the shorter the boat the more it handles like a coracle, ie. doesn't want to run straight.

willk · 23 July 2020, 11:30

Quote:

Originally Posted by jwalker

I'm with willk...

Socially Distanced, in case anyone gets the wrong impression

BoatyMacBoatface · 23 July 2020, 12:47

Thanks guys, that's been really useful as my logic just wasn't working on that format at all ��

My other question is this...

Would there be a noticable speed/performance output between a 3.2m with a 15hp and a 3.8m with a 20hp out

Will a 3.2m be much slower than the 3.8m with a 20hp which isn't it maximum outboard power rating... but the 3.2m is at its maximum rating?

As you can probably tell im.tryingbto squeeze the maximum speed out of a boat/outboard combination. This is because I will cover alot of distance with the boat and want to spend as little time doing it so I can maximise my productivity

paddlers · 23 July 2020, 12:55

The longer boat will handle better. After that it's all about weight and weight distribution with tiller extensions etc coming into play . The increased area of the 3.8 will allow it to 'skim' across the surface rather than plough through like the smaller boat.

jeffstevens763@g · 23 July 2020, 12:58

Quote:

Originally Posted by BoatyMacBoatface

Thanks guys, that's been really useful as my logic just wasn't working on that format at all ��

My other question is this...

Would there be a noticable speed/performance output between a 3.2m with a 15hp and a 3.8m with a 20hp out

Will a 3.2m be much slower than the 3.8m with a 20hp which isn't it maximum outboard power rating... but the 3.2m is at its maximum rating?

As you can probably tell im.tryingbto squeeze the maximum speed out of a boat/outboard combination. This is because I will cover alot of distance with the boat and want to spend as little time doing it so I can maximise my productivity

ive found about a 2 knot difference for 5 hp standard props, but having said that if you start re propping you can get a tad more especially with stainless props but then you need a tacho to find out your WOT RPM to start with. also you can find you drop off the plain very easily if too high pitched and differing weights being carried. ive propped down to get a more crisp response in the chop to keep on the plane for longer and back on quicker.

Fenlander · 23 July 2020, 14:11

>>>I'm trying to squeeze the maximum speed out of a boat/outboard combination.

In truth over the past ten years using SIBS around 3.2-3.8m with 15-20hp motors the typical UK sea state is often the limiting factor and around 15kts might be a maximum comfortable speed. You will get that with every 15-20hp combo.

A year or so back we ran a 20hp motor on our 3.8m... we now have a 15hp and because we've lost one person from our crew the speeds are broadly the same. As Jeff says go up 5hp with the same load and 2-3kts is about all the improvement you'll see.

Steve509926 · 23 July 2020, 19:09

Being new to sib's myself I know the dilemma you have regarding size of sib, size of engine, speed etc. In my opinion the other things to consider are packed size, packed weight, where your using it and what your using it for.
After trawling through the internet and reading forums, I had my mind set on a Honwave t38 and a 20HP Tohatsu/Mercury, that was until I saw things in the flesh. The t38 might be a great sib for some but not for me, I needed something with a much flatter deck.
The good guys on this forum suggested I take a look at the Excel Volaire 390.
I took a trip to Sutton Coalfield and had a good look at the Excel sib's. I have to say I was impressed, good quality and keen pricing. However the Volaire 390, despite being very impressive and tempting, is in my opinion, huge! I would struggle with the weight and size on my own. To cut a long story short, I ended up buying the Volante SD360. Great internal space, flat airdeck, just the right size to fit in my Navara with OB and all the other gear I will be taking with me, and last but not least manageable on my own - and from your point of view will take a 20HP outboard.
I can't comment on how it is on the water as I only inflated it today, maiden voyage will be the first week in August!

BoatyMacBoatface · 24 July 2020, 22:20

After listening to the advice of the knowledgeable members on here I've decided to go for the T38 and use the existing 20hp outboard in the garage... so thanks everyone for helping me make sense of it all.

The next question is where will I get the best deal on a new Howave T38 IE2 and launch wheels?

Steve509926 · 24 July 2020, 23:04

When I looked at the Honwave t38 last month, Liverpool Power Boats appeared to be the most competitive.