Weight of motor on transom

[pundy14]

Hi all,

Have a HH V16 that I've converted to a side console. Full rebuild, new everything with shipwright rating transom to 190kg.

Currently has 4 stroke Merc 90hp (185kg).

My issue is how low the stern sits. Water doesn't lap the splash well, but get's awfully close. If there was a small swell blowing inwards, there would be water coming into the splash well.

I'm told the 16's always sat low and that it's a performance hull not a fishing hull etc. I also know I have shifted the center of flotation likely back a bit given the console sits further towards the stern than the original would have been, and with strengthening the transom, perhaps there is more weight anyway.

I am looking at a 70hp Yammy that weighs 125kg, so a saving of 60kg.

I am also looking to drain the underfloor tank as part of the tank does extend further towards the stern.

Question - is a 60kg (maybe 70/80kg with the empty tank) saving likely to make a significant difference to how the boat sits?

end build 1.jpgRebuild motor fitting.jpgboat sit low 1.jpg

[tunaticer]

From the photo in the water I think you need to relocate about 100kg to the bow if you keep the 90.
Fit a 90 litre live well in the fore deck if you can relocate fuel tank and batteries forward.
Get the lecky mounted and it's batteries forward will go a long way towards levelling it out.
Dropping to the 70 will help but you might be left wanting a bit more power.

[pundy14]

The issue I have is there isn’t really anything else I can move from the stern. There is the starter battery, and the engine (hydraulic steering etc).


The only other weigh stern of centre is probably 30-40% of a 90ltr under floor tank and obviously the drivers seat.


Eventually elec motor, another battery, stainless bow rail, some safety gear will be at the bow. But that will only bring the nose down, not the stern up right?


Agree - 70 seems about the lowest id go. But not sure what other option I have? The issue I have is there isn’t really anything else I can move from the stern. There is the starter battery, and the engine (hydraulic steering etc).

The only other weigh stern of centre is probably 30-40% of a 90ltr under floor tank and obviously the drivers seat.


Eventually elec motor, another battery, stainless bow rail, some safety gear will be at the bow. But that will only bring the nose down, not the stern up right?


Agree - 70 seems about the lowest id go. But not sure what other option I have?

[tunaticer]

You could raise the forward face of your wash well to the gunwhale height, then you could ignore the problem altogether.
A bit of ply and fibreglass and gelcoat....it is an option.

[pundy14]

Thanks Tuna - So you mean build the back of the transom higher so the water needs to come up further to get into the splash well?

Is that safe?

[tunaticer]

The wall closest to you when in the boat, not the wall at the outboard.
Let the wash well fill and drain, just stop it coming into the cockpit.

[ranmar850]

Gee, I'd be concerned about the freeboard at the rear, not just the low height of the transom. Small deep vees like the Haines don't carry weight well. The effect of moving weight fore and aft isn't always obvious. Your logitudinal COG comes into it. Putting 60 kg in the bow to try to counter the effect of 60 kg right at the transom isn't always a one-for-one deal.And remember you are adding to overall weight. If you can move the entire 60kg forward, not necessarlly all the way to the bow, even just to amidships, can result in a large change. This is real marine architect stuff. And I ain't one of them, just learnt by observation and making mistakes over the years. Oh, and knowing how to do actual stability calcs, required for the ticket I had, don't ask me to do them now

[Dignity]

I've seen Haines fairly low in the transom but that is ridiculously low in the water. The old girls are notorious for weight distribution causing this sort of issue. I have seen where a half cabin was changed to a CC successfully but there was a significant change in weight distribution with where the fuel tank was located (well forward) etc. I know with my previous boat I had to change where I stored my ice etc as I weigh 70 kg but all my crew were at least 110kg. Made balancing any boat interesting, a haines even more so.

[Noelm]

Ranmar is correct, do not just add weight to the bow, a boat is not a seesaw pushing the bow down, doesn’t always raise the stern, you have to MOVE weight or remove weight from the back.

[ranmar850]

Exactly how close is the fuel tank to amidships? And how much does it hold? Did you enlarge your fuel capacity when you did the rebuild? You are heading in the right direvtion, I think, when you are talking about draining the underfloor tank for starters. I'd do that, and rig up an ordinary portable tank, situated in the bow, and see how that affects things.
If you are unsure about how to drain the tank, I've found a method which has worked well for me with a number of different boats. It involves the VERY GENTLE application of compressed air . I stress the gentle part of it--you are not pressure testing your tank. Find the easiest way to get an air nozzle into the breather or filler . Breather might be easiest, means you just leave the filler cap on. If not, you have to block the filler ( pull hose off, insert bolt) and put the air nozzle into the filler with a rag stuffed around it. Extend your fuel line down into a jerry can, out through the bung is best,gently introduce air pressure until the fuel starts to flow. Again, i stress gentle. When it slows down, a touch more air.
If you want to experiment with moving weight around, apart from the fuel, 20 litre containers of water are really useful. If the draining of the tank, then moving weight around sorts things out, you may be faced with horrible reality of pulling up that lovely new floor and moving the existing tank/having a new tank built to shift that weight permanently.

[pundy14]

Thanks for the replies all - great insight.

I think my first tests going from lease invasive to most invasive:

1. Add weight in bow to see what (if at all) impact on how it sits in water. I understand this likely wont have any impact on stern.
2. Drain underfloor tank, rig up portable tank in bow for now and see impact.
3. Change to lighter motor, from 185kg to 125kg.
4. Cut out underfloor tank.
5. Pod/hull extension to increase buoyancy.

Question re the tank. It's a 90ltr alu tank that starts from the base of the casting deck, and extends to about the stern side of the captains chair. So it does extend past the midship, which is probably smack bang where the console is. The tank itself surely wouldn't weigh more than 20-30kg empty?

It has to be the tank + heavy 4 stroke right? The rebuild certainly hasn't added significant weight from original I wouldn't have thought?

Also - I should confirm. There is no water of any kind in the hull. It is completely dry with all cavities under the floor able to flow liquid to the under floor and sub floor bungs. The hull is as solid/dry as a rock. The transom itself is 25 inch (originally 20).

It's frustrating and anxiety inducing given the effort/resources I've put into this thing. I'm hoping a 75hp 4 stroke and an empty tank does the trick

[Noelm]

Do just go by motor HP, check the weights of them, Mercury in the 70-90HP weigh a ton, Yamaha 70 is a feather weight, Suzuki 90-100 are quite light too. That said, you are fighting an uphill battle, those skinny deep V Haines are notorious for your issue, but there is lots of them around with big motors on them. Building a flotation style pod MIGHT be OK, it could also be a lot of work for minimal improvement and possible unknown performance.

[ranmar850]

Sounds like a plan. One step at a time. You have the right attitude, some just dive into the hardest/most invasive/most expensive first.

[Mopheus]

Did you weigh the bare hull before and after refurbishment? The overall attitude doesn't look too stern-heavy IMO; it just seems to have significantly less freeboard overall. I'd be questioning whether the rebuild itself has added significant hull weight.

Here's a random V16R off Boatsales for comparison - outboard is a Tomatsu 90hp 2-stroke so about 50kg lighter on the stern, but sitting with similar attitude; just with a bunch more freeboard overall.

[NAGG]

Taking some weight out of the stern will help ..... no doubt

A heavy outboard vs a light weight makes a huge difference

I have a 480 hornet with a 75 merc .... a big ass heavy motor

I've owned the same hull with a 60hp yammi = totally different aspect - it's the weight is the problem .

A light weight yammi 70 would be the right choice for that hull

find the best way to remove Kgs off the transom - lighter motor first & foremost


Chris