Before I add a hydrofoil would like advice...slow speed porpoise

[WA-Newb]

I have only had our new boat (38 year old 15ft tri-hull) out one real time but am very eager to take it out again the minute I have the time. Before I take it out I wanted to try and address the slow speed porpoising which makes it very difficult to see over the bow and uncomfortable all around. At high speed (3/4 throttle and up) it is fine and does not bounce etc. but if I am trying to go slow as in fog and maintain around 1/3 throttle it just goes up in the air and when I let off the throttle the water comes a bit over the stern. So in the fog I can either not see over the bow or go too fast to see anyway.

My question is this...I bought a hydrofoil to try but when I noticed the existing holes did not line up I thought I would make sure I needed one of these before drilling another set of holes. That being said this boat did have a fin of some kind installed at one point. This motor came with the boat I believe since I got the owners manuals etc. from the original owners family member

BUT...maybe I am just overweight on the stern since I have two full tanks (6 gallons each) two batteries a 50 HP and a 10 HP kicker....if that's the case will the hydrofoil still work?

I am not sure how else to load the boat since the stern is where all this stuff needs to be while trolling.

The boat is rated for up to 85 HP.

Also...my prop has one fin that looks to have hit a rock or something and is bent over and tore about a half inch...would this cause anything undesirable? Would I notice a difference with a new prop?

Thank you.

 

[emoney]

Re: Before I add a hydrofoil would like advice...slow speed porpoise

Where's the pin set on the the motor, is it towards the bottom or the top? Also, are you getting up on plane and then slowing down or are you trying to plane "slowly"? Does sound like you've got quite a bit of weight in the stern, especially if it's just you on the boat. If you take someone else, might be better to have that person move to the bow until she's planed.

 

[jestor68]

Re: Before I add a hydrofoil would like advice...slow speed porpoise

One of these will have your 15 ft boat planing nicely at very slow speeds. It is called the Doel fin.


If your prop is badly dinged up, you should replace it.

 

[WA-Newb]

Re: Before I add a hydrofoil would like advice...slow speed porpoise

Where's the pin set on the the motor, is it towards the bottom or the top? Also, are you getting up on plane and then slowing down or are you trying to plane "slowly"? Does sound like you've got quite a bit of weight in the stern, especially if it's just you on the boat. If you take someone else, might be better to have that person move to the bow until she's planed.

Here is a photo of where the pin currently sits...not sure which way (if any) I should try to move it.
Wish I didn't have to pull it out of the water to move the pin but maybe I should try moving it before drilling the extra holes for the fins.

I am new to boating so I am not sure if I am trying to plane slowly or not...I guess I just want to go mid speed and be able to see over the bow..lol When we went out (the only time) it was foggy real bad and either I was going so fast I felt like I was gonna run into something or I was plowing with my butt in the water and bow up in the air.

Had a boat right next to me when I decided to WOT all the way in tot he dock (was hoping and assuming he had GPS) and when we docked he said he was impressed with how my boat planed so nicely...I am not sure why he commented on it though..maybe since it's an old tri-hull? I told him about the bow raising up at low speeds and he said to run..not walk to go get a set of fins / hydrofoils since his boat did the same thin until he got them.

I have read many many posts etc. and looks like they may work for some and not for others...I am just trying to make sure I am at least trying to solve it without the so called band aid.

And Jestor..the one I bought that I am ready to possibly install is the Atwood set that is supposed to raise up out of the water when I am on plane for less drag...that's all I know about it vs. others. I only got it because it was cheap, local...and can be returned if it sucks (good ole wal-mart...lol)

 

[jestor68]

Re: Before I add a hydrofoil would like advice...slow speed porpoise

My recommendation is to return it to Wally world and get the one and only(original) Doel fin. Since the holes don't line up, it's possible the previous owner had one on there and removed it to use on his next boat.

Just google "Doel fin" to find out who carries it. One that I know of is Bass Pro Shops. It costs just $40.

Your pin setting looks fine. When you get a Doel fin on there, you'll likely be able to raise it one hole higher(back) to gain more top speed and still plane off quickly.

You need to take the drain plug out whenever the boat is out of the water; to let any water in the bilge(bottom of boat) drain out.

 

[steelespike]

Re: Before I add a hydrofoil would like advice...slow speed porpoise

I'm not crazy about adding foils to help performance because you still have a problem under the foil bandaid.
Sure would be nice if you could balance the load better.I figure your boat dry weight is probably 700 lbs.
In round figures you have about 500 lbs concentrated in the stern don't know how any boast could do well with that setup.
i did have Doelfins on an 18ft 3.0 I/O and a 15ft Startcraft 50 hp outboard.
They did do exactly what they advertised.
The foil that is out of the water at speed sounds interesting. Though if the motor height is right the Doelfin should be close to being out of the water.

 

[spdracr39]

Re: Before I add a hydrofoil would like advice...slow speed porpoise

Fix the prop first and see what happens this is a must. Next check the pins that adjust the angle the motor is mounted. It might need to tilt in towards the transom a little more if it doesn't help you can put it back. Finally if that doesn't fix it drill the new holes in the fin not the anti-cav plate. The fins enhance performance (sometimes) but won't fix a bad setup. If you don't fix the main issue it will never have optimal performance.

 

[WA-Newb]

Re: Before I add a hydrofoil would like advice...slow speed porpoise

I am just on a quick break...been painting father in laws exterior of large house every waking moment since he only has the lift there until Sunday. Wanted to add a link to the fin I got...last night saw that there was only 4 reviews but all 5 stars.
http://www.amazon.com/gp/product/B0...=1789&creative=390957&creativeASIN=B001O0D6RO

Also..is a prop replacement something that involves any special tools or skills?
Isn't there some seals in there that I need a puller for etc.?

I will look more into the Doel Fin as well.
Thanks.

 

[steelespike]

Re: Before I add a hydrofoil would like advice...slow speed porpoise

Is it possible you could at least store one gas tank at the bow or even midway forward
at least while traveling to your fishing hole.
why 2 batteries" Don't you troll with the kicker?
With all that weight in the stern its possible the boat could be over powered in a serious following sea.
Especially if a beefy friend moved to the stern at the wrong time.

 

[WA-Newb]

Re: Before I add a hydrofoil would like advice...slow speed porpoise

Ugh...one more day to go on the 12 hour days of painting then hopefully a day off to play on the water again. Hope I am not to burned out (and sunburned) to even enjoy taking the new boat out.

Is it possible you could at least store one gas tank at the bow or even midway forward
at least while traveling to your fishing hole.
why 2 batteries" Don't you troll with the kicker?
With all that weight in the stern its possible the boat could be over powered in a serious following sea.
Especially if a beefy friend moved to the stern at the wrong time.

Steel...I had to google what you meant by following sea and now that you said that I remember while we were out some swells came from out of nowhere that dang near rolled right over the stern of the boat while we were going slow (bow up). So that is a good point now that I am thinking of it.

I guess I could probably buy some gas line and put one of the tanks up front...and the extra battery will be going away as soon as I check the charging system and kicker. I just don't want to be out and get surprised right now being this inexperienced so since i had another battery thought I should throw it in there as a backup.

Hopefully Monday I will get the time to go see how this thing sits in the water at the dock...we didn't even look at that since we were so excited to get the motor running and to get out and try to fish for the first time.

If all goes well and I get the time I will try to take pics and possibly a video so I can have one to compare if I go the hydrofoil route.
I have seen others ask to see before and after pics or videos but personally haven't found any yet so maybe it will help others who wonder if the fins work. Again..I want to try the non fin route first but sure seems to be the "thing" to get according to many people so far.

I would still like to know if a prop is hard to install or if it's a matter of taking the nut off and sliding the old one off and the new one on.

 

[goat lady]

Re: Before I add a hydrofoil would like advice...slow speed porpoise

Ugh...one more day to go on the 12 hour days of painting then hopefully a day off to play on the water again. Hope I am not to burned out (and sunburned) to even enjoy taking the new boat out.



Steel...I had to google what you meant by following sea and now that you said that I remember while we were out some swells came from out of nowhere that dang near rolled right over the stern of the boat while we were going slow (bow up). So that is a good point now that I am thinking of it.

I guess I could probably buy some gas line and put one of the tanks up front...and the extra battery will be going away as soon as I check the charging system and kicker. I just don't want to be out and get surprised right now being this inexperienced so since i had another battery thought I should throw it in there as a backup.

Hopefully Monday I will get the time to go see how this thing sits in the water at the dock...we didn't even look at that since we were so excited to get the motor running and to get out and try to fish for the first time.

If all goes well and I get the time I will try to take pics and possibly a video so I can have one to compare if I go the hydrofoil route.
I have seen others ask to see before and after pics or videos but personally haven't found any yet so maybe it will help others who wonder if the fins work. Again..I want to try the non fin route first but sure seems to be the "thing" to get according to many people so far.

I would still like to know if a prop is hard to install or if it's a matter of taking the nut off and sliding the old one off and the new one on.

you may need a prop with a lower pitch. I fish at night and had to get a prop with a lower pitch to stay on plane at a slower speed. as for changing the prop it isn't hard to do, just remove big nut, take your hands and pull the old prop off, and slide the new one back on, tighten big nut back on, I think it will torque at 55lb, thats what I torque my 90 hp mercury at and it works fine. hope this helps.

 

[WA-Newb]

Re: Before I add a hydrofoil would like advice...slow speed porpoise

just remove big nut, take your hands and pull the old prop off, and slide the new one back on, tighten big nut back on, I think it will torque at 55lb, thats what I torque my 90 hp mercury at and it works fine. hope this helps.

Does your prop have all this stuff behind it?


I was scared all this would either need to be pulled or it would just fall out once I pulled the prop off and I would be stuck seeking help again...lol

 

[steelespike]

Re: Before I add a hydrofoil would like advice...slow speed porpoise

If your thinking of moving one tank and adding a hose why not move both.
Its almost like a 200 lb change.Your removing about 100 lbs from the stern and adding it at the bow.
Its sure to feel different. If the battery ois just backup it seems you could place it anywhere even if only part way forward.
I know you don't have a whole lot of time or energy right now but as time allows:
It would also help if you gave us an organized run down of your boat,motor, prop size(usually under the prop nut)
present light load wot rpm and speed by gps.Does the boat have power trim?

 

[WA-Newb]

Re: Before I add a hydrofoil would like advice...slow speed porpoise

I am so sore and burned out I couldn't even get up to go try my boat / attempt to fish on my only day off.
Just typing this is hurting..lol

This may sound like a stupid question but I was wondering if a 100 pound change from stern to middle of the boat (under front built in seats) would be the same as if I added a 200 pound person and had him ride in the seat.

Maybe I shouldn't try to type before having coffee but what I was thinking was to have my buddy sit in the bow and see if that makes a difference or improvement...he weighs around 210. If it did then I could take the battery and the 12 gallons of gas and store them under that bench / seat.

Steel...I don't have a tach or GPS yet so know way to tell how fast I am going (really hoping to find both cheap enough for me to get).
I will look at prop size today...the load of the boat is two batteries, a 50 HP and a 10 HP...two 6 gallon gas tanks (all in the stern) and other than that just fishing gear and required safety devices really. The two people in the boat will have a combined weight of about 280 (equally split). And no power trim.

 

[WA-Newb]

Re: Before I add a hydrofoil would like advice...slow speed porpoise

Just looked at my prop size....

Current one that has a small dent / ding is 13 3/4 x 15.

I have a new one sitting here that is 13 1/4 x 17.

Can anyone tell me what the difference (if any) on performance would be if I used the new one vs. the old one.

 

[WA-Newb]

Re: Before I add a hydrofoil would like advice...slow speed porpoise

Well it looks like I need to get a tach gauge before proceeding with a prop replacement

Just searched for info on props and read this...

-------------------------
Examples:
A 21 pitch prop turns 4200 RPM on your boat, but 4600 is the upper RPM limit. Try a 19" pitch prop to shift down" and increase your RPMs. If your outboard is turning 6100 RPMs and your red line is 5600, "shift up" and try a prop with 2" more pitch and test again.

Propellers are labeled diameter x pitch. (A 13x19 prop is 13" in diameter and is 19" pitch)

diameter - the distance (in inches) across the circle made by the blade tips as the propeller rotates.
pitch - the distance (in inches) a prop moves forward with one 360? revolution (assuming zero slip).
--------------------------

Still need to learn about this and put some brain power into it (which I am definitely lacking today).

 

[goat lady]

Re: Before I add a hydrofoil would like advice...slow speed porpoise

Does your prop have all this stuff behind it?
View attachment 158376

I was scared all this would either need to be pulled or it would just fall out once I pulled the prop off and I would be stuck seeking help again...lol

only the prop will come off, there is a washer behind the prop that you can pull off. but you don't have to remove it to change the prop. just pull the prop off and push new one back on the shaft and replace big nut and tighten it to 55lb of torque.

 

[goat lady]

Re: Before I add a hydrofoil would like advice...slow speed porpoise

Just looked at my prop size....

Current one that has a small dent / ding is 13 3/4 x 15.

I have a new one sitting here that is 13 1/4 x 17.

Can anyone tell me what the difference (if any) on performance would be if I used the new one vs. the old one.

what ever your rpm's are at wot with the 15pitch it should drop about 400 rpm's with the 17 pitch. for each number you go up in pitch, your engine should drop about 200 rpm's and for each number of pitch you go down, your engine should go up about 200 rpm's I hope this helps.

 

[ondarvr]

Re: Before I add a hydrofoil would like advice...slow speed porpoise

First off, what you described as porpoising is not porpoising, it's just bow rise and is normal for just about any boat as it transitions from low speed to a higher speed and begins to plane. There are things you can do to limit the bow rise, but you won't eliminate it completely. Moving things forward is easy and cheap, changing the prop to a lower pitch may help, but if your RPMs aren't correct (too high) with the new prop you still have problems. The lower pitch really only shortens the time spent in transition, it won't do much to reduce the bow rise if that is the speed you want to go, it's like down shifting in car. There are many different types of props though and each type will yield slightly different results.

A foil will sort of help, but isn't the best option, trim tabs will help limit the bow rise and allow you to stay on plane at a lower speed.

Also check the floatation foam located under the floor, it can become waterlogged over time and increase the weight a great deal, this will contribute to the problems you described.

 

[steelespike]

Re: Before I add a hydrofoil would like advice...slow speed porpoise

Short answer,your new 17" pitch will further aggravate your your difficulties.
You need to check regulations putting tanks in an inclosed area also putting batteries with them is not a good idea.
You may be able to ventilate the seat some how.