Underpowered and hard to plane

[TraskRiver]

Hey guys,
I just acquired a 1995 18.5' alumaweld sea skiff (center console)
It has a 40hp 2 stroke merc and a 9.9 4 stroke merc. Got it out on the water today to test some things out and it will barely plane the boat. It was me and one other passenger. Fuel cell is up front and nothing other than some life vests and a few fishing poles in the boat. Just a big turd on the water to be honest. As far as I know, everything is original in the boat. There is a visual bend on one of the prop fins and the fin itself is completely polished aluminum from spending it's whole life running sand bars in the bay. So, being I can't afford to upgrade the power and it needs a new prop anyway... can someone shed some light on a prop that may help the higher rpm's and planing out without losing low end power? I don't have a tack and have not figure what the rpms at full throttle are yet but the motor seems to run good and strong.

Also, if anyone can find the information on this boat that would tell me what the max hp motor it can have that would be great just for future reference. I cannot seem to find it or a picture of a boat that is similar to this one. Ill get some pictures of it tomorrow. The front of the boat has a lot of lift almost resembling a drift boat. It is registered as a 1995 alumaweld 18.5' and says " sea skiff" on the side of the boat.

 

[Mi duckdown]

There should be a plate on the transom that tells you Max hp, weight and all that stuff. My .02? Your are WAY under powered. Sorry. Call/ google, Alumaweld for specs.

 

[steelespike]

We need to know the year of the motor, Prop size(probably under the prop nut). wot rpm and the gps speed.An induction tach is reasonable and easy to install.
Some cells have a gps app.Once we have baseline numbers we can go from there.

 

[Texasmark]

I'm with Mr. Duck on this. 40 hp on an 18+ boat with another engine hanging off the transom, even if it is aluminum is seriously underpowered. I can remember the FILs 14' FG runabout of the 60's era. Boat weighed all of 600#, 40 horse Rude, 6 gallon tank, 1 size 24 battery and about 100# of gear. 25 was tops and with planing speed at around 15, you were just barely making it. Question is, how did the PO do with it from the time it was new? Maybe that's why it was for sale.....got tired of putting along.

Mark

 

[TraskRiver]

There should be a plate on the transom that tells you Max hp, weight and all that stuff. My .02? Your are WAY under powered. Sorry. Call/ google, Alumaweld for specs.

It is definitely under powered. The plate is there but completely sun faded and not eligible. I have googled what I could to no avail, next step is to call alumaweld.

We need to know the year of the motor, Prop size(probably under the prop nut). wot rpm and the gps speed.An induction tach is reasonable and easy to install.
Some cells have a gps app.Once we have baseline numbers we can go from there.

Gotcha.
I figured that is the best way to determine prop sizing. But being the prop that is on there is original and has a pretty good bend in one of the fins, I figured it may be irrelevant? And was going to either have this one fixed or pick up a new one. I will locate the prop size and post back. Also, I will try and pin an rpm and speed on the boat next time I take it out.
Can't seem to find any matching serial numbers to reference charts on numerous websites I have looked at.
2 stroke 40hp 4cyl elect. start with power tilt, Serial number 0G297835
They should be the same year as the boat (95) as they were bought with it new.

I'm with Mr. Duck on this. 40 hp on an 18+ boat with another engine hanging off the transom, even if it is aluminum is seriously underpowered. I can remember the FILs 14' FG runabout of the 60's era. Boat weighed all of 600#, 40 horse Rude, 6 gallon tank, 1 size 24 battery and about 100# of gear. 25 was tops and with planing speed at around 15, you were just barely making it. Question is, how did the PO do with it from the time it was new? Maybe that's why it was for sale.....got tired of putting along.

Mark

Agreed that it is under powered...It is welded aluminum and a pretty heavy boat. Most of the 18' alumawelds I see have either a 90 or 115 on them.

I just acquired it and don't have the funds to bump the power up at this moment but possibly in the future. For now, it needs a new prop so I figure maybe try and see if that could help for now.

The boat came from my parents. It was bought to run in the bay for crabbing. And that is just what it has done it's whole life. It has never once (until now) been in fresh water. It is pretty well kept. Motors always flushed with fresh water and boat and gear always rinsed with fresh water after each use.

I was with them when they bought it new back in 95-96ish and they had the smaller engine put on from the dealer to save money and knowing it was just for crabbing in the bay. I don't think it has ever even seen full throttle until I had it on the river yesterday.

 

[jestor68]

The prop selector calls for a 9 or 10 pitch prop. The bent blade will hurt performance.

Get a new prop.

 

[midcarolina]

IMO......Since you are so far under powered I would make darn sure the motor is not sitting too deep in the water.......and get a doel fin,

Now I know you are going to get many stay away from hydrofoil reply's............but in your situation I see little choice.

 

[steelespike]

Present day 18s are 115 hp.1995s weigh 990 lbs. If they were just putting around they may never have bothered to prop right.

 

[TraskRiver]

Cavitation plate is near level with the hull and seems to be the right height. Wasn't aware of a "doel fin" until mentioned.
Steel, I put a call in to the manufacturer today about the boats max hp rating. It's max is 80hp in the book. But he also informed me that the 75, 90 and 115 4 stroke mercs all weight exactly the same at 399lb and it is not uncommon for boat owners to exceed the hp recommendations and that most 18' do run 75-115hp. But, on another note, this particular boat has a shallow transom height of 20". The current motor weights in around 175lbs? I think. So, even going to a 75h 4 stroke EFI would be putting on an extra 220lbs on the rear. Taking on water over the transom be an issue at that point with the added weight?

Other option if I were to shop for a new motor is to stick with a 2 stroke to keep the weight down. Just shop for a used 75-90hp 2 stroke? New motor would be a year out at best

For now I have to stick with a new prop.

 

[Mi duckdown]

Task. a doel fin will only hurt you IMHO And a different prop is a waste of money Unless it beat to heck. MORE HP

 

[TraskRiver]

Task. a doel fin will only hurt you IMHO And a different prop is a waste of money Unless it beat to heck. MORE HP

The prob has a bad bend in one of the blades and some other small dings.


So i figure new prop, why not try and get one to help it plane out

 

[midcarolina]

Task. a doel fin will only hurt you IMHO And a different prop is a waste of money Unless it beat to heck. MORE HP

Please elaborate on why in this specific situation a hydrofoil is a bad idea?

 

[jestor68]

Task. a doel fin will only hurt you IMHO And a different prop is a waste of money Unless it beat to heck. MORE HP

To the uninitiated, the Doel Fin is exactly what a under powered boat needs to help get it up on plane at a considerably slower speed.

At the speeds his combination is capable of, it should actually help the overall performance, including more top speed.

 

[Mi duckdown]

So NOW you tell Us the the Prop is BAD.??? WT hell

 

[TraskRiver]

Sorry for the confusion.
See first post

There is a visual bend on one of the prop fins and the fin itself is completely polished aluminum from spending it's whole life running sand bars in the bay. So, being I can't afford to upgrade the power and it needs a new prop anyway... can someone shed some light on a prop that may help the higher rpm's and planing out without losing low end power?

Second post

But being the prop that is on there is original and has a pretty good bend in one of the fins, I figured it may be irrelevant? And was going to either have this one fixed or pick up a new one.

And again in the second post

For now, it needs a new prop so I figure maybe try and see if that could help for now.

Intention of the thread was being that the boat is under powered and in need of a new prop anyway, what would be a good prop to help it plane out until I can upgrade the motor.

 

[jestor68]

I already checked the Mercury prop selector, and (like I posted before) it said a 9 or 10 pitch Black Max aluminum or Vengeance(SS) prop.

How does that compare to what you are running now?

 

[steelespike]

If they were running in shallows often making contact with sand the prop may actually be worn undersize diameter.
I think a 9" pitch is a good bet if we are making a pick without a base line test. Perhaps a 4 blade.

 

[steelespike]

I'm with Mr. Duck on this. 40 hp on an 18+ boat with another engine hanging off the transom, even if it is aluminum is seriously underpowered. I can remember the FILs 14' FG runabout of the 60's era. Boat weighed all of 600#, 40 horse Rude, 6 gallon tank, 1 size 24 battery and about 100# of gear. 25 was tops and with planing speed at around 15, you were just barely making it. Question is, how did the PO do with it from the time it was new? Maybe that's why it was for sale.....got tired of putting along.

Mark

If you want to talk under powered. circa 1952 I was 9 and we had a tired old 1930s 15' Thompson with a 5 hp Firestone as the Family boat to get
the 3 off us to the island with food,clothes etc in preparation of a summer stay.
Nit too much later we had a 14 hp Evinrude on the old Thompson it seemed like it might fly.

 

[hwsiii]

Trask, what steele is saying about a 4 blade prop is 100% right. You will need a Solas Amita 4 blade prop to help pick the stern up for a much better planning attitude. You now have a boat with 2 motors on the stern with a woefully underpowered 40 HP motor, and there is no worse place to have that extra weight than on the very stern of the boat. You need to take that smaller motor off of the boat to do all of your tests for maximum speed, which should be about 20 to 25 MPH at top speed.

You also need to take some pictures of the stern of the boat and where the anti ventilation plate is located compared to the bottom of the boat.
If you will go to this posting it will show you what I am talking about and give you more information.

http://forums.iboats.com/forum/gener...ersus-aluminum



H

 

[Texasmark]

Go back to near the top and re-read Steelspike's "gotta haves". Once you do that he can run the numbers against a prop slip calculator and make a fairly close guess for the pitch of your replacement prop. If you don't have a tach, buy a "Tiny Tach". He needs the WOT rpm number with your current prop even if it is damaged.

Mark