New Engine for 4 mtr Humber Assault.

[p-morgan]

Hi i currently have a Yamaha 2001 F30 4 stroke on my 4 mtr Humber assault.
Its a great motor but manual start and trim. I was looking to modernise and go a new or nearly new. Should I stay with a 30 hp or got say 40 hp.
I was thinking a new Tohatsu.

Now weights the 30 Yam is 93 Kgs
the 30 Tohatsu 78 - 80 kgs
the 40 Tohatsu is 98 kgs

I spoke to Humber regarding the transom weight and max HP for the 4 mtr assault.
Its 95 Kg where as the 4.3 is 105 kgs.
The guy at Humber said the 40 Tohatsu at 98 would be fine but just inform my insurer.

But I was thinking a lighter outboard with the same hp would improve performance. Would the extra 10 hp really make a big difference. Or would dropping 15 Kg be better and give room to add weight in the form of dive gear.

Sorry for the long post but some one on here must have had similar saturation.

Cheers Paul.

[jeffstevens763@g]

The 40 will give you far more in performance than the weight saving.Ron Hale Marine Ltd - Yamaha F40FE Y-COP

84 kg

[Stevem]

The 4m assault can take a 50 looking at Humber website. Tohatsu 50 tldi would fit the spec. I have just put one on an sr4 and am loving it. Ive not worked out the fuel burn yet but it appears to be excellent.

[p-morgan]

Originally Posted by Stevem

The 4m assault can take a 50 looking at Humber website. Tohatsu 50 tldi would fit the spec. I have just put one on an sr4 and am loving it. Ive not worked out the fuel burn yet but it appears to be excellent.

I was looking at 4stroke max transom weight is 95 kgs for 4m assault. I would like power trim tilt remote electric start. Humber said i could go to 98kgs hence the Tohatsu MFS40.

I just checked the Yamaha F40FEDL 40hp Outboard Engine some folks say its 83 while others say 100Kg,s thats a fair difference.

[jeffstevens763@g]

F40 | Yamaha Motor Australia

98kg with power trim and tilt

[p-morgan]

Originally Posted by jeffstevens763@g

F40 | Yamaha Motor Australia

98kg with power trim and tilt

Like i said the guy at humber said it was ok as the 4.3mtr transom is the same but has a load rating of 105.
I currently have a mercury 3.5 kicker on but am happy to go without if I fit a new 4 stroke 30/40 motor. We are a pretty tight community and there is always some out if the worst happened, easy to get a tow

[eze]

Hi Guys,


Quick questions here,
1 - Going from a 30 hp to a 40 hp.....How many more knots will that achieve on a typical 4 Metre deep hull rib such as a Humber assault?
2 - Will a 2s or 4s give quicker acceleration?
3 - An outboard engine power increase should be +50% to seen noticeable performance?


thanks


eze

[Poly]

Originally Posted by eze

Hi Guys,


Quick questions here,
1 - Going from a 30 hp to a 40 hp.....How many more knots will that achieve on a typical 4 Metre deep hull rib such as a Humber assault?
2 - Will a 2s or 4s give quicker acceleration?
3 - An outboard engine power increase should be +50% to seen noticeable performance?


thanks


eze

1. It depends. But the assault isn't really a deep V hull anyway.
2. The two stroke
3. Is that a question? It seems an odd statement. For a start it would depend how marginal the old engine is, if it struggles to get a heavy load on the plane in some conditions you will notice even small increments. If you rarely sit at max throttle and the engine doesn't work hard then why upgrade at all.

[p-morgan]

Originally Posted by Poly

1. It depends. But the assault isn't really a deep V hull anyway.
2. The two stroke
3. Is that a question? It seems an odd statement. For a start it would depend how marginal the old engine is, if it struggles to get a heavy load on the plane in some conditions you will notice even small increments. If you rarely sit at max throttle and the engine doesn't work hard then why upgrade at all.

For me the upgrade was for electric start and trim /tilt. its currently got a 2001 Yamaha 4s 30 hp. its the same block as the 40hp but lighter due to lack of TT and ES.
I use my rib for diving typically two divers full kit. It does struggle a wee bit. not getting anywhere near wot.

My theory was lighter more morden engine same HP should be light years on the old motor.

[jeffstevens763@g]

There's so much more to it than HP hull, weight distribution , prop, engine set up to list a few when I have the choice I go for the biggest HP the boat allows that will give you redundancy most of the time. 2 st vs 4 st a matter of choice for me 2st stinks but the new generation doesn't by all accounts I still wouldn't buy one OMO.
Be prepared to swap props if your going to change weight in a big way ( carrying divers)

[Poly]

Originally Posted by p-morgan

For me the upgrade was for electric start and trim /tilt. its currently got a 2001 Yamaha 4s 30 hp. its the same block as the 40hp but lighter due to lack of TT and ES.

I use my rib for diving typically two divers full kit. It does struggle a wee bit. not getting anywhere near wot.



My theory was lighter more morden engine same HP should be light years on the old motor.

If it's the same block I'd certainly try to find the funds for the bigger engine. I think you'll notice going 30-40. That said if you currently aren't able to get the right revs you are propped wrong, so could possibly improve things for about £100!

[eze]

Originally Posted by Poly

1. It depends. But the assault isn't really a deep V hull anyway.
2. The two stroke
3. Is that a question? It seems an odd statement. For a start it would depend how marginal the old engine is, if it struggles to get a heavy load on the plane in some conditions you will notice even small increments. If you rarely sit at max throttle and the engine doesn't work hard then why upgrade at all.

Tis a question, My reason for asking is this.

If I increase the power on my car/motorbike from say 100 hp to 125hp then for me, my seat of pants dyno barely registers any discernible gains. If however I increase to 150hp (50% increase) then the gains are noticeable in the seat of pants dyno. I was just wondering how any increases in hp relate in the world of ribs for general use (not racing)

I hope this explains my 'odd question'

I could go on to ask considering the capital investment, is it prudent to go from 30 to 40hp or would it be wise to go for 50hp in this particular instance?






cheers

eze

[jeffstevens763@g]

If you go on the Suzuki web site they have performance figures for certain craft with different HP engines as a guide OMO but go as big as you can afford or the boat can take

[eze]

Originally Posted by jeffstevens763@g

If you go on the Suzuki web site they have performance figures for certain craft with different HP engines as a guide OMO but go as big as you can afford or the boat can take

Will Do Jeff

[Poly]

Originally Posted by eze

Tis a question, My reason for asking is this.

If I increase the power on my car/motorbike from say 100 hp to 125hp then for me, my seat of pants dyno barely registers any discernible gains. If however I increase to 150hp (50% increase) then the gains are noticeable in the seat of pants dyno. I was just wondering how any increases in hp relate in the world of ribs for general use (not racing)

I hope this explains my 'odd question'

Generally though we don't drive our cars the same way we drive boats. the reality of driving on public roads means there is lots of relatively gentle acceleration, some mid range revs and then bobbing along in a high hear with low revs, and repeat the process. Rarely do you ever drive at full throttle, and even more rarely for any prolonged period. Your car can probably go a lot faster than you chose to drive it at.

In contrast ribs used for pleasure are often accelerated hard, and frequently sit at high revs. If you are in a hurry you will sit at full throttle for long periods. If its lumpy you may be on and off the throttle a lot but hard.

I could go on to ask considering the capital investment, is it prudent to go from 30 to 40hp or would it be wise to go for 50hp in this particular instance?

Difficult for anyone else to answer. It depends as much on your financial position and frequency of usage. There are guys on here who are comfortably well off and who go out every weekend who would see that as a no brainer. There are others who count the fuel usage because it has to be carefully budgeted and who have other life commitments that mean they would be sacrificing something else to do it.